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Sample records for andes centrales del

  1. Tectonics of the central Andes

    NASA Technical Reports Server (NTRS)

    Bloom, Arthur L.; Isacks, Bryan L.; Fielding, Eric J.; Fox, Andrew N.; Gubbels, Timothy L.

    1989-01-01

    Acquisition of nearly complete coverage of Thematic Mapper data for the central Andes between about 15 to 34 degrees S has stimulated a comprehensive and unprecedented study of the interaction of tectonics and climate in a young and actively developing major continental mountain belt. The current state of the synoptic mapping of key physiographic, tectonic, and climatic indicators of the dynamics of the mountain/climate system are briefly reviewed.

  2. LANDSAT imagery of the Central Andes

    NASA Technical Reports Server (NTRS)

    Komer, C. A.; Morgan, P.

    1986-01-01

    The central Andes of South America extend from approximately 14 deg. S to 28 deg. S as an unbroken chain of mountains and volcanoes over 2000 km long. It is here that the Nazca plate dives under the South American plate at angles varying from 10 deg to 30 deg. Very little is known about the volcanoes comprising this classic, subduction-type plate margin. A catalogue of the volcanoes in the central Andes is being prepared by Dr. P.W. Francis and Dr. C.A. Wood at the NASA Lunar and Planetary Institute. At present, more than 800 volcanoes of Cenozoic age have been recognized in the chain, with an estimated 75-80 major, active Quarternary volcanoes. Approximately one hundred 1536 x 1536 pixel color composite Optronics positives were produced from six full LANDSAT Thermatic Mapper scenes and three partial TM scenes. These positives cover a large portion of the central Andes. The positives were produced from LANDSAT data using the VAX imaging package, LIPS. The scenes were first transferred from magnetic tape to disk. The LIPS package was then used to select volcanically interesting areas which were then electronically enhanced. Finally, the selected areas were transferred back to tape and printed on the Optronics equipment. The pictures are color composites using LANDSAT TM bands 7,4, and 2 in the red, green, and blue filters, respectively.

  3. Evidencing decadal and interdecadal hydroclimatic variability over the Central Andes

    NASA Astrophysics Data System (ADS)

    Segura, Hans; Carlo Espinoza, Jhan; Junquas, Clementine; Takahashi, Ken

    2016-09-01

    In this study we identified a significant low frequency variability (8 to 20 years) that characterizes the hydroclimatology over the Central Andes. Decadal-interdecadal variability is related to the central-western Pacific Ocean (R 2 = 0.50) and the zonal wind at 200 hPa above the Central Andes (R 2 = 0.66). These two oceanic-atmospheric variables have a dominant decadal-interdecadal variability, and there is a strong relationship between them at a low frequency time scale (R 2 = 0.66). During warming decades in the central-western Pacific Ocean, westerlies are intensified at 200 hPa above the Central Andes, which produce decadal periods of hydrological deficit over this region. In contrast, when the central-western Pacific Ocean is cooler than usual, easterly anomalies prevail over the Central Andes, which are associated with decades of positive hydrological anomalies over this region. Our results indicate that impacts of El Niño on hydrology over the Central Andes could be influenced by the low frequency variability documented in this study.

  4. Crustal-thickness variations in the central Andes

    SciTech Connect

    Beck, S.L.; Myers, S.C.; Wallace, T.C.; Zandt, G. |; Silver, P.G.; Drake, L.

    1996-05-01

    We estimated the crustal thickness along an east-west transect across the Andes at lat 20{degree}S and along a north-south transect along the eastern edge of the Altiplano from data recorded on two arrays of portable broadband seismic stations (BANJO and SEDA). We found crustal-thickness variations of nearly 40 km across the Andes. Maximum crustal thicknesses of 70-74 km under the Western Cordillera and the Eastern Cordillera thin to 32-38 km 200 km east of the Andes in the Chaco Plain. The central Altiplano at 20{degree}S has crustal thicknesses of 60 to 65 km. The crust also appears to thicken from north (16{degree}S, 55-60 km) to south (20{degree}S, 70-74 km) along the Eastern Cordillera. The Subandean zone crust has intermediate thicknesses of 43 to 47 km. Crustal-thickness predictions for the Andes based on Airy-type isostatic behavior show remarkable overall correlation with observed crustal thickness in the regions of high elevation. In contrast, at the boundary between the Eastern Cordillera and the Subandean zone and in the Chaco Plain, the crust is thinner than predicted, suggesting that the crust in these regions is supported in part by the flexural rigidity of a strong lithosphere. With additional constraints, we conclude that the observation of Airy-type isostasy is consistent with thickening associated with compressional shortening of a weak lithosphere squeezed between the stronger lithosphere of the subducting Nazca plate and the cratonic lithosphere of the Brazilian craton. 26 refs., 4 figs.

  5. Crustal-thickness variations in the central Andes

    NASA Astrophysics Data System (ADS)

    Beck, Susan L.; Zandt, George; Myers, Stephen C.; Wallace, Terry C.; Silver, Paul G.; Drake, Lawrence

    1996-05-01

    We estimated the crustal thickness along an east-west transect across the Andes at lat 20°S and along a north-south transect along the eastern edge of the Altiplano from data recorded on two arrays of portable broadband seismic stations (BANJO and SEDA). Waveforms of deep regional events in the downgoing Nazca slab and teleseismic earthquakes were processed to isolate the P-to-S converted phases from the Moho in order to compute the crustal thickness. We found crustal-thickness variations of nearly 40 km across the Andes. Maximum crustal thicknesses of 70 74 km under the Western Cordillera and the Eastern Cordillera thin to 32 38 km 200 km east of the Andes in the Chaco Plain. The central Altiplano at 20°S has crustal thicknesses of 60 to 65 km. The crust also appears to thicken from north (16°S, 55 60 km) to south (20°S, 70 74 km) along the Eastern Cordillera. The Subandean zone crust has intermediate thicknesses of 43 to 47 km. Crustal-thickness predictions for the Andes based on Airy-type isostatic behavior show remarkable overall correlation with observed crustal thickness in the regions of high elevation. In contrast, at the boundary between the Eastern Cordillera and the Subandean zone and in the Chaco Plain, the crust is thinner than predicted, suggesting that the crust in these regions is supported in part by the flexural rigidity of a strong lithosphere. With additional constraints, we conclude that the observation of Airy-type isostasy is consistent with thickening associated with compressional shortening of a weak lithosphere squeezed between the stronger lithosphere of the subducting Nazca plate and the cratonic lithosphere of the Brazilian craton.

  6. Altiplano-Puna volcanic complex of the central Andes

    NASA Technical Reports Server (NTRS)

    De Silva, S. L.

    1989-01-01

    A model is presented accounting for many features of the Altiplano-Puna volcanic complex situated in the Central Volcanic Zone of the Andes which contains 50 recently active volcanoes. The dominant elements of the complex are several large nested caldera complexes which are the source structures for the major regionally distributed ignimbrite sheets that characterize the complex. The study of the complex reveals the importance of the intersection of subsidiary axis-oblique tectonic trends related to regional stress fields peculiar to individual oceanic ridge sections with the axis-parallel trends predominant at all spreading centers in localizing hydrothermal discharge zones.

  7. Two scales of inflation at Lastarria-Cordon del Azufre volcanic complex, central Andes, revealed from ASAR-ENVISAT interferometric data

    NASA Astrophysics Data System (ADS)

    Froger, J.-L.; Remy, D.; Bonvalot, S.; Legrand, D.

    2007-03-01

    ASAR-ENVISAT Interferometric Synthetic Aperture Radar (InSAR) data collected over the Lastarria-Cordon del Azufre complex (Chile-Argentina) between March 2003 and May 2005 show the persistence of the large wavelength ground inflation revealed by Pritchard and Simons in 2002 from the analysis of ERS InSAR data [Nature 418 (2002) 167-170]. After reducing the tropospheric contribution in the interferograms using a combination of data network adjustment and analysis of MODIS images, we produced an accurate interferometric time series showing a 2 yr long temporal evolution of the ground displacements patterns. Two distinct inflating signals are detected. The main signal covers an elliptical area with a 45 km NNE-SSW major axis and a 37 km minor axis. It is correlated with a regional topographic dome. We estimated its maximum inflation rate to ˜ 2.5 cm yr - 1 . We inverted the InSAR data for a range of source geometries (spherical, prolate ellipsoids, penny-shaped cracks). The inferred source parameters for 2003-2005 period are consistent with an over-pressured reservoir at shallow to intermediate crustal depths (7-15 km), with an average volumetric rate of inflation of about 14 × 10 6 m 3 yr - 1 . In addition to this main signal a new feature highlighted by the ASAR data is short wavelength inflation (6 km wide) at the location of Lastarria volcano on the northern margin of the large wavelength signal. We explain this short wavelength signal by a spherical over-pressured source lying 1000 m below the summit of Lastarria volcano. We estimate the average volumetric rate of inflation during the observation period to be ˜ 35 × 10 3 m 3 yr - 1 . It is remarkable that both volumetric variations for the large and small inflations exhibit the same evolution during the 2003-2005 period, suggesting that both processes could be related. On the basis of the inversion results and of arguments provided by field evidences and a morpho-structural analysis of the Digital Elevation

  8. Seismic Imaging of a Nascent Batholith in the Central Andes

    NASA Astrophysics Data System (ADS)

    Ward, K. M.; Zandt, G.; Beck, S. L.; Christensen, D. H.; Mcfarlin, H. L.

    2013-12-01

    Cordilleran mountain belts, such as the modern central Andes and Mesozoic western North American Cordillera formed in regions of significant upper plate compression and were punctuated by high flux magmatic events that coalesced into large composite batholiths. Unlike the North American Cordillera, compressive mountain building is still active in the central Andes and any large modern batholith still at depth must be inferred from surface volcanics and geophysical data. In the Andes it has been suggested that a modern batholith exists beneath the Altiplano-Puna Volcanic Complex (APVC), the location of a 11-1 Ma ignimbrite flare-up, however, the magmatic underpinnings has only been geophysically investigated in a few widely spaced locations and a migmatite zone of crustal melt with minimal mantle input remains a viable competing interpretation. We present new high-resolution 3-D seismic images of the APVC crust based on a joint inversion of ambient noise surface-wave dispersion data and receiver functions from broadband stations and identify a shallow (<20 km depth) low-velocity body that we interpret as a magmatic mush zone, the Altiplano-Puna Mush Body (APMB). Below the APMB, we observe near-vertical zones of low velocity that bifurcate near the base of the crust with one arm of low velocity migrating under the main volcanic arc and a second separate arm of low velocity below the voluminous backarc volcanism. Previous attenuation tomography studies have traced these zones through the mantle where they intersect the top of the subducting Nazca slab at locations with elevated seismic activity, providing strong evidence that the deeper near-vertical zones of low velocity we are imaging are related to dewatering of the slab and associated mantle-sourced melt pathways. Based on these considerations, we suggest the ~200 km diameter and ~20 km thick body is a nascent silicic batholith compatible with the magma mush model of batholith formation. The direct imaging of this

  9. Paleomagnetism of Permian and Triassic rock, central Chilean Andes

    NASA Astrophysics Data System (ADS)

    Forsythe, Randall D.; Kent, Dennis V.; Mpodozis, Constantino; Davidson, John

    The first paleomagnetic data from Permian and Triassic formations west of the Andean divide are presented. Four formations of Permian or Triassic age in the central Chilean Andes have been investigated: two are located in the coastal ranges, and two are in the main cordillera. Of the formations in the main cordillera (Pastos Blancos and Matahuaico formations), only the Pastos Blancos Formation has yielded characteristic directions. While a fold test is absent, magnetizations are most likely secondary and yield pre-tilt corrected concordant inclinations, but yield declinations discordant 30° clockwise in comparison to the South American apparent polar wander path. Both formations from the coastal ranges (Cifuncho and Pichidangui formations) yielded stable directions. Postfolding magnetizations in the Cifuncho Formation also show declinations discordant 30° clockwise and concordant inclinations. The Pichidangui Formation has two stable components: one of postfolding age is concordant to apparent polar wander path data, and one of probable prefolding (Late Triassic) age is concordant in declination, but discordant in inclination. Further work is needed to better define the prefolding magnetizations in the Pichidangui Formation, but at present these preliminary results are the first paleomagnetic signs of displaced terranes along the Pacific margin of Chile. If correct, the results suggest that the Pichidangui Formation was some 15° of latitude farther south during the Late Triassic and had likely moved northward to its present latitudinal position with respect to cratonic South America by Middle to Late Jurassic.

  10. Tectonic control on denudation rates in the central Bolivian Andes

    NASA Astrophysics Data System (ADS)

    Zeilinger, Gerold; Kober, Florian; Hippe, Kristina; Lendzioch, Theodora; Grischott, Reto; Pillco Zolá, Ramiro; Christl, Markus

    2013-04-01

    Effects of a positive feedback loop between erosion and tectonics have been shown by analogue and numerical models and have been inferred from field observations at the scale of mountain ranges. We present new data from the Bolivian Andes supporting these observations, although common geomorphic parameters do not indicate a simple correlation. The upper Rio Grande segment, located between Cochabamba, Santa Cruz and Sucre, drains a major catchment in the central Bolivian Cordillera, from the Eastern Cordillera (EC) in the W, through the Interandean Zone (IAZ) and the Subandes (SA) in the E. The catchment covers an area of 58939 km² with an altitude range from 400 to 5150 m above sea level. Geologically, the Bolivian Andes comprise (from W to E) the Altiplano, the EC, the IAZ and the SA fold and thrust belts. The Altiplano represents an almost perfectly closed basin with distinct barriers defined by the Western Cordillera and Eastern Cordillera. The Rio Grande does not reach the Altiplano (unlike Rio La Paz and Rio Consata) but has its western drainage divide along the high peaks of the EC that experienced a period of intense shortening between Late Oligocene and Miocene. Near Cochabamba, the EC comprises metasedimentary siliciclastic rocks of Ordovician age. These rocks are overlain by Cretaceous to Paleocene and / or Neogene sediments with an angular unconformity. The IAZ and SA form an east-vergent fold and thrust belt and comprise Paleozoic and Mesozoic units. Farther east, the structures of the SA progressively include Neogene foreland strata of the Chaco foreland basin. The Chaco basin rests on the Brazilian shield east of the Subandean Belt and forms the modern foreland basin, where the lower Rio Grande catchment is sited. We obtained 58 cosmogenic 10Be catchment wide denudation rates for the Rio Grande catchments upstream of Abapó. They range from 7 mm/kyr to 1550 mm/kyr thus integrating at maximum over the last 10.000 years, with a mean of 262 mm/kyr. In

  11. The nature of orogenic crust in the central Andes

    NASA Astrophysics Data System (ADS)

    Beck, Susan L.; Zandt, George

    2002-10-01

    The central Andes (16°-22°S) are part of an active continental margin mountain belt and the result of shortening of the weak western edge of South America between the strong lithospheres of the subducting Nazca plate and the underthrusting Brazilian shield. We have combined receiver function and surface wave dispersion results from the BANJO-SEDA project with other geophysical studies to characterize the nature of the continental crust and mantle lithospheric structure. The major results are as follows: (1) The crust supporting the high elevations is thick and has a felsic to intermediate bulk composition. (2) The relatively strong Brazilian lithosphere is underthrusting as far west (65.5°W) as the high elevations of the western part of the Eastern Cordillera (EC) but does not underthrust the entire Altiplano. (3) The subcrustal lithosphere is delaminating piecemeal under the Altiplano-EC boundary but is not completely removed beneath the central Altiplano. The Altiplano crust is characterized by a brittle upper crust decoupled from a very weak lower crust that is dominated by ductile deformation, leading to lower crustal flow and flat topography. In contrast, in the high-relief, inland-sloping regions of the EC and sub-Andean zone, the upper crust is still strongly coupled across the basal thrust of the fold-thrust belt to the underthrusting Brazilian Shield lithosphere. Subcrustal shortening between the Altiplano and Brazilian lithosphere appears to be accommodated by delamination near the Altiplano-EC boundary. Our study suggests that orogenic reworking may be an important part of the "felsification" of continental crust.

  12. Bayesian spatiotemporal interpolation of rainfall in the Central Chilean Andes

    NASA Astrophysics Data System (ADS)

    Ossa-Moreno, Juan; Keir, Greg; McIntyre, Neil

    2016-04-01

    Water availability in the populous and economically significant Central Chilean region is governed by complex interactions between precipitation, temperature, snow and glacier melt, and streamflow. Streamflow prediction at daily time scales depends strongly on accurate estimations of precipitation in this predominantly dry region, particularly during the winter period. This can be difficult as gauged rainfall records are scarce, especially in the higher elevation regions of the Chilean Andes, and topographic influences on rainfall are not well understood. Remotely sensed precipitation and topographic products can be used to construct spatiotemporal multivariate regression models to estimate rainfall at ungauged locations. However, classical estimation methods such as kriging cannot easily accommodate the complicated statistical features of the data, including many 'no rainfall' observations, as well as non-normality, non-stationarity, and temporal autocorrelation. We use a separable space-time model to predict rainfall using the R-INLA package for computationally efficient Bayesian inference, using the gridded CHIRPS satellite-based rainfall dataset and digital elevation models as covariates. We jointly model both the probability of rainfall occurrence on a given day (using a binomial likelihood) as well as amount (using a gamma likelihood or similar). Correlation in space and time is modelled using a Gaussian Markov Random Field (GMRF) with a Matérn spatial covariance function which can evolve over time according to an autoregressive model if desired. It is possible to evaluate the GMRF at relatively coarse temporal resolution to speed up computations, but still produce daily rainfall predictions. We describe the process of model selection and inference using an information criterion approach, which we use to objectively select from competing models with various combinations of temporal smoothing, likelihoods, and autoregressive model orders.

  13. Characteristics of Precipitation Features and Annual Rainfall during the TRMM Era in the Central Andes

    NASA Technical Reports Server (NTRS)

    Mohr, Karen I.; Slayback, Daniel; Yager, Karina

    2014-01-01

    The central Andes extends from 7 deg to 21 deg S, with its eastern boundary defined by elevation (1000m and greater) and its western boundary by the coastline. The authors used a combination of surface observations, reanalysis, and the University of Utah Tropical Rainfall Measuring Mission (TRMM) precipitation features (PF) database to understand the characteristics of convective systems and associated rainfall in the central Andes during the TRMM era, 1998-2012. Compared to other dry (West Africa), mountainous (Himalayas), and dynamically linked (Amazon) regions in the tropics, the central Andes PF population was distinct from these other regions, with small and weak PFs dominating its cumulative distribution functions and annual rainfall totals. No more than 10% of PFs in the central Andes met any of the thresholds used to identify and define deep convection (minimum IR cloud-top temperatures, minimum 85-GHz brightness temperature, maximum height of the 40-dBZ echo). For most of the PFs, available moisture was limited (less than 35mm) and instability low (less than 500 J kg(exp -1)). The central Andes represents a largely stable, dry to arid environment, limiting system development and organization. Hence, primarily short-duration events (less than 60 min) characterized by shallow convection and light to light-moderate rainfall rates (0.5-4.0 mm h(exp -1)) were found.

  14. Evolution of crustal thickening in the central Andes, Bolivia

    NASA Astrophysics Data System (ADS)

    Eichelberger, Nathan; McQuarrie, Nadine; Ryan, Jamie; Karimi, Bobak; Beck, Susan; Zandt, George

    2015-09-01

    Paleoelevation histories from the central Andes in Bolivia have suggested that the geodynamic evolution of the region has been punctuated by periods of large-scale lithospheric removal that drive rapid increases in elevation at the surface. Here, we evaluate viable times and locations of material loss using a map-view reconstruction of the Bolivian orocline displacement field to forward-model predicted crustal thicknesses. Two volumetric models are presented that test assumed pre-deformation crustal thicknesses of 35 km and 40 km. Both models predict that modern crustal thicknesses were achieved first in the northern Eastern Cordillera (EC) by 30-20 Ma but remained below modern in the southern EC until ≤10 Ma. The Altiplano is predicted to have achieved modern crustal thickness after 10 Ma but only with a pre-deformation thickness of 50 km, including 10 km of sediment. At the final stage, the models predict 8-25% regional excess crustal volume compared to modern thickness, largely concentrated in the northern EC. The excess predicted volume from 20 to 0 Ma can be accounted for by: 1) crustal flow to the WC and/or Peru, 2) localized removal of the lower crust, or 3) a combination of the two. Only models with initial crustal thicknesses >35 km predict excess volumes sufficient to account for potential crustal thickness deficits in Peru and allow for lower crustal loss. However, both initial thickness models predict that modern crustal thicknesses were achieved over the same time periods that paleoelevation histories indicate the development of modern elevations. Localized removal of lower crust is only necessary in the northern EC where crustal thickness exceeds modern by 20 Ma, prior to paleoelevation estimates of modern elevations by 15 Ma. In the Altiplano, crustal thicknesses match modern values at 10 Ma and can only exceed modern values by 5 Ma, post-dating when modern elevations were thought to have been established. Collectively, these models predict that

  15. Contrasting response of glacierized catchments in the Central Himalaya and the Central Andes to climate change

    NASA Astrophysics Data System (ADS)

    Ragettli, Silvan; Pellicciotti, Francesca; Immerzeel, Walter

    2015-04-01

    The Andes of South America and the Himalaya in high-mountain Asia are two regions where advanced simulation models are of vital importance to anticipate the impacts of climate change on water resources. The two mountain systems hold the largest ice masses outside the polar regions. Major rivers originate here and downstream regions are densely populated. In the long run, glacier recession generates concerns about the sustainability of summer runoff. This study benefits from recent efforts of carefully planned short-term field experiments in two headwater catchments in the Central Andes of Chile and in the Central Himalaya in Nepal. The two study catchments contrast in terms of their climate and in the characteristics of their glaciers. A systematic approach is developed, built upon the available local data, to reduce the predictive uncertainty of a state-of-the-art glacio-hydrological model used for the projection of 21st century glacier changes and catchment runoff. The in-situ data are used for model development and step-wise, multivariate parameter calibration. Catchment runoff and remotely sensed MODIS and Landsat snow cover are used for model validation. The glacio-hydrological model simulates the water cycle with a high temporal (hourly time steps) and spatial (100 m grid cells) resolution and accounts for processes typical of both regions like glacier melt under debris cover or mass redistribution through avalanching. Future projections are based on the outputs of twelve stochastically downscaled global climate models for two emission scenarios (RCP 4.5 and RCP 8.5). This is one of the first truly intercomparative modeling studies at the catchment scale across mountain regions of the world to assess and compare future changes in glaciers and snow cover and associated impacts on streamflow production. Both catchments will experience significant glacier mass loss throughout the twenty-first century. However, the trajectories of simulated future runoff and

  16. Late Tertiary northwestward-vergent thrusting in Valle del Cauca, Colombian Andes

    SciTech Connect

    Alfonso, C.A.; Sacks, P.E.; Secor, D.T. Jr.; Cordoba, F.

    1989-03-01

    The Valle del Cauca is a topographic basin situated between the Cordillera Central and the Cordillera Occidental in the Colombian Andes. The basement is Mesozoic mafic igneous rock of the Volcanic and Amaime Formations and clastic sediments and chert of the Espinal and Cisneros Formations. The basement was intruded by middle Cretaceous granodiorites (including the Batolito de Buga) and was deformed and metamorphosed to greenschist facies. The Mesozoic rocks originated in an oceanic setting and were accreted to northwestern South America during the Cretaceous or early Tertiary. Unconformably overlying the Mesozoic basement are the Eocene and Oligocene Vijes (marine limestone) and Guachinte and Cinta de Piedra (fluvial and deltaic sandstone and mudstone). In the Cordillera Central, the Cinta de Piedra is unconformably overlain by fanglomerate of the Miocene La Paila Formation. These clastics coarsen and thicken eastward. Geologic mapping and structural analyses show that the Mesozoic basement and its Tertiary cover are faulted and folded. Folds are asymmetric and overturned westward. Faults dip at shallow to moderate angles to the east and carry older sedimentary or basement rocks westward over younger rocks.

  17. The Largest Holocene Eruption of the Central Andes Found

    NASA Astrophysics Data System (ADS)

    Fernandez-Turiel, J.; Rodriguez-Gonzalez, A.; Saavedra, J.; Perez-Torrado, F.; Carracedo, J.; Osterrieth, M.; Carrizo, J.; Esteban, G.

    2013-12-01

    We present new data and interpretation about a major eruption -spreading ˜110 km3 ashes over 440.000 km2- long thought to have occurred around 4200 years ago in the Cerro Blanco Volcanic Complex (CBVC) in NW Argentina. This eruption may be the biggest during the past five millennia in the Central Volcanic Zone of the Andes, and possibly one of the largest Holocene eruptions in the world. The environmental effects of this voluminous eruption are still noticeable, as evidenced by the high content of arsenic and other trace elements in the groundwaters of the Chacopampean Plain. The recognition of this significant volcanic event may shed new light on interpretations of critical changes observed in the mid-Holocene paleontological and archaeological records, and offers researchers an excellent, extensive regional chronostratigraphic marker for reconstructing mid-Holocene geological history over a wide geographical area of South America. More than 100 ashes were sampled in Argentina, Chile and Uruguay during different field campaigns. Ash samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), grain size distributions laser diffraction, and geochemically by electron microprobe (EMPA) and laser ablation-HR-ICP-MS. New and published 14C ages were calibrated to calendar years BP. The age of the most recent CBVC eruption is 4407-4093 cal y BP, indirectly dated by 14C of associated organic sediment within the lower part of a proximal fall deposit of this event (26°53'16.05"S-67°44'48.68"W). This is the youngest record of a major volcanic event in the Southern Puna. This age is consistent with other radiocarbon dates of organic matter in palaeosols underlying or overlying distal ash fall deposits. Based on their products, all of rhyolitic composition, we have distinguished 8 main episodes during the evolution of the most recent CBVC eruption: 1) the eruption began with a white rhyolite lava dome extrusion; 2) followed by a Plinian

  18. Deformation, deposition, and surface uplift in the hinterland of the Central Andes, Bolivia

    NASA Astrophysics Data System (ADS)

    Leier, A.; McQuarrie, N.; Garzione, C. N.; Eiler, J. M.

    2011-12-01

    Paleoelevation histories from mountain belts like the Central Andes of Bolivia provide important constraints on the timing and geodynamic mechanisms associated with surface uplift. New stable isotope data from paleosol carbonate nodules in the Altiplano and Eastern Cordillera of the Central Andes of Bolivia indicate a previously undocumented episode of surface uplift occurred in the region between ca. 24 and 17 Ma. Oxygen isotope and clumped-isotope thermometry values from paleosol carbonate in strata >24 Ma suggest paleoelevations as low as sea-level. Paleosol carbonate in strata ca. 17 Ma have oxygen isotope and clumped-isotope thermometry values, which using modern lapse rates, indicate an increase in elevation of approximately 3 km. Relatively undeformed Oligocene and Miocene strata overlap faulted Paleozoic rocks of the Bolivian Eastern Cordillera, indicating deposition and surface uplift post-dated and was decoupled from upper crustal deformation. Together, geological data from the area record an initial period of deformation and exhumation, a subsequent period of sediment deposition and overlap, and then an episode of surface uplift that was not accompanied by upper crustal deformation. We propose accommodation for the Oligocene-Miocene strata was associated with mantle and lowermost crustal processes, and the subsequent increase in surface elevation was an isostatic response to removal of dense material through delamination or drip. Combined with existing data sets in the Central Andes, these new data suggest multiple, regionally-variable, and diachronous periods of surface uplift occurred within the Central Andes during the Cenozoic Era.

  19. A Uniform Conductivity Image along the Chilean Margin? Observations from the Central and Southern Andes

    NASA Astrophysics Data System (ADS)

    Brasse, H.; Soyer, W.

    2001-12-01

    Over the last years a reasonably detailed image of electrical conductivity distribution has been achieved in the central Andes at latitudes 20--22oS. These studies have been complemented by recent magnetotelluric investigations in the southern Chilean Andes (39oS). Despite the different subduction settings concerning e.g., age of subducted plate, trench filling and history of volcanic arcs, the inferred conductivity distributions show remarkable similarities. Higher conductivities assumed to be connected with hydration-dehydration processes are only resolved as a 2nd order effect at larger depths above the downgoing slab. On the other hand, large margin-subparallel fault zones presumably originating from oblique subduction are consistently imaged as good conductors in the mid crust, e.g., the Atacama Fault and the West Fissure in the central Andes and the Liquiñe-Ofqui Fault in the south. The main differences concerning electrical properties between the two subduction settings include the large conductivity anomaly below the Altiplano high plateau in the central Andes and an anisotropic forearc crust in the south, indicated by ystematic deflection of induction arrows. An explanation of the latter phenomenon may possibly be seen in fossil, Cenozoic or even Pre-Andean structures.

  20. Ancient ice islands in salt lakes of the Central Andes

    USGS Publications Warehouse

    Hurlbert, S.H.; Chang, Cecily C.Y.

    1984-01-01

    Massive blocks of freshwater ice and frozen sediments protrude from shallow, saline lakes in the Andes of southwestern Bolivia and northeastern Chile. These ice islands range up to 1.5 kilometers long, stand up to 7 meters above the water surface, and may extend out tens of meters and more beneath the unfrozen lake sediments. The upper surfaces of the islands are covered with dry white sediments, mostly aragonite or calcite. The ice blocks may have formed by freezing of the fresh pore water of lake sediments during the "little ice age." The largest blocks are melting rapidly because of possibly recent increases in geothermal heat flux through the lake bottom and undercutting by warm saline lake water during the summer.

  1. Ancient ice islands in salt lakes of the central andes.

    PubMed

    Hurlbert, S H; Chang, C C

    1984-04-20

    Massive blocks of freshwater ice and frozen sediments protrude from shallow, saline lakes in the Andes of southwestern Bolivia and northeastern Chile. These ice islands range up to 1.5 kilometers long, stand up to 7 meters above the water surface, and may extend out tens of meters and more beneath the unfrozen lake sediments. The upper surfaces of the islands are covered with dry white sediments, mostly aragonite or calcite. The ice blocks may have formed by freezing of the fresh pore water of lake sediments during the "little ice age." The largest blocks are melting rapidly because of possibly recent increases in geothermal heat flux through the lake bottom and undercutting by warm saline lake water during the summer.

  2. U/Pb ages on detrital zircons in the southern central Andes Neogene foreland (36°-37°S): Constraints on Andean exhumation

    NASA Astrophysics Data System (ADS)

    Sagripanti, Lucía; Bottesi, Germán; Naipauer, Maximiliano; Folguera, Andrés; Ramos, Victor A.

    2011-12-01

    U/Pb dating on detrital zircons was performed in the Pampa de Carrizalito depocenter of the Late Miocene foreland basin associated with the Southern Central Andes orogenic front. This reveals Andean and pre-Andean components in magmatic derived zircons inhomogeneously distributed through the sequence. Andean, Grenville, Pampean, Famatinian and Gondwanic components reveal a complex source distribution from either the Main Andes, Coastal Cordillera and basement foreland areas. These are discussed showing different patterns in the context of the Andean orogenic cycle. Cretaceous and Jurassic components that are partly related to Mesozoic batholiths, developed at the western slope of the Andes at these latitudes, have a very contrasting behavior through the sequence: While Jurassic grains are represented from base to top, Cretaceous ones dilute upwardly. This is explained through the progressive uplift of the Southern Central Andes that could have created a barrier to Cretaceous and Jurassic detritus, while the older ones could have had either an alternative source area represented by the inverted rift system of the Huincul Ridge in the foreland area and the Cordillera del Viento in the hinterland area or the reworking of Jurassic sedimentary sequences of the Neuquén basin. Finally, a progressive enrichment in pre-Andean components to the top of the sequence is interpreted as related to the development of a broken foreland and the consequent rapid expansion of the orogenic front at the time of development of a slab shallowing setting in the region as shown by previous works.

  3. Epidemiology of Echinococcus granulosus infection in the central Peruvian Andes.

    PubMed Central

    Moro, P. L.; McDonald, J.; Gilman, R. H.; Silva, B.; Verastegui, M.; Malqui, V.; Lescano, G.; Falcon, N.; Montes, G.; Bazalar, H.

    1997-01-01

    The prevalence of human, canine, and ovine echinococcosis was determined in an endemic area of the Peruvian Andes where control programmes have not been operational since 1980. Prevalence of infection in humans was determined using portable ultrasound, chest X-rays, and an enzyme-linked immunoelectrotransfer blot (EITB) assay. Canine and ovine echinococcal prevalence was determined by microscopic stool examinations following arecoline purging for tapeworm detection and by examination of the viscera from slaughtered livestock animals, respectively. The prevalence among 407 humans surveyed was 9.1%. The frequency of disease in the liver, lung, and in both organs was 3.4%, 2.0%, and 0.2%, respectively. Portable ultrasound or portable chest X-ray has shown that, compared to adults, children under 11 years had significantly higher seropositive rates without evidence of hydatid disease (P < 0.05). Among the 104 dogs inspected for echinococcus after arecoline purging, 33 (32%) were positive for adult tapeworms. Among the 117 sheep slaughtered at the local abattoir, 102 (87%) had hydatid cysts. The prevalence of human hydatidosis in this endemic area of Peru is one of the highest in the world and nearly five times higher than previously reported in 1980. An increase in echinococcosis prevalence may result after premature cessation of control programmes. PMID:9509628

  4. Prediction of extreme floods in the eastern Central Andes based on a complex networks approach

    NASA Astrophysics Data System (ADS)

    Boers, N.; Bookhagen, B.; Barbosa, H. M. J.; Marwan, N.; Kurths, J.; Marengo, J. A.

    2014-10-01

    Changing climatic conditions have led to a significant increase in the magnitude and frequency of extreme rainfall events in the Central Andes of South America. These events are spatially extensive and often result in substantial natural hazards for population, economy and ecology. Here we develop a general framework to predict extreme events by introducing the concept of network divergence on directed networks derived from a non-linear synchronization measure. We apply our method to real-time satellite-derived rainfall data and predict more than 60% (90% during El Niño conditions) of rainfall events above the 99th percentile in the Central Andes. In addition to the societal benefits of predicting natural hazards, our study reveals a linkage between polar and tropical regimes as the responsible mechanism: the interplay of northward migrating frontal systems and a low-level wind channel from the western Amazon to the subtropics.

  5. Glaciological studies in the central Andes using AIRSAR/TOPSAR

    NASA Technical Reports Server (NTRS)

    Forster, Richard R.; Klein, Andrew G.; Blodgett, Troy A.; Isacks, Bryan L.

    1993-01-01

    The interaction of climate and topography in mountainous regions is dramatically expressed in the spatial distribution of glaciers and snowcover. Monitoring existing alpine glaciers and snow extent provides insight into the present mountain climate system and how it is changing, while mapping the positions of former glaciers as recorded in landforms such as cirques and moraines provide a record of the large past climate change associated with the last glacial maximum. The Andes are an ideal mountain range in which to study the response of snow and ice to past and present climate change. Their expansive latitudinal extent offers the opportunity to study glaciers in diverse climate settings from the tropical glaciers of Peru and Bolivia to the ice caps and tide-water glaciers of sub-polar Patagonia. SAR has advantages over traditional passive remote sensing instruments for monitoring present snow and ice and differentiating moraine relative ages. The cloud penetrating ability of SAR is indispensable for perennially cloud covered mountains. Snow and ice facies can be distinguished from SAR's response to surface roughness, liquid water content and grain size distribution. The combination of SAR with a coregestered high-resolution DEM (TOPSAR) provides a promising tool for measuring glacier change in three dimensions, thus allowing ice volume change to be measured directly. The change in moraine surface roughness over time enables SAR to differentiate older from younger moraines. Polarimetric SAR data have been used to distinguish snow and ice facies and relatively date moraines. However, both algorithms are still experimental and require ground truth verification. We plan to extend the SAR classification of snow and ice facies and moraine age beyond the ground truth sites to throughout the Cordillera Real to provide a regional view of past and present snow and ice. The high resolution DEM will enhance the SAR moraine dating technique by discriminating relative ages

  6. Morphologic evolution of the Central Andes of Peru

    NASA Astrophysics Data System (ADS)

    Gonzalez, Laura; Pfiffner, O. Adrian

    2012-01-01

    In this paper, we analyze the morphology of the Andes of Peru and its evolution based on the geometry of river channels, their bedrock profiles, stream gradient indices and the relation between thrust faults and morphology. The rivers of the Pacific Basin incised Mesozoic sediments of the Marañon thrust belt, Cenozoic volcanics and the granitic rocks of the Coastal Batholith. They are mainly bedrock channels with convex upward shapes and show signs of active ongoing incision. The changes in lithology do not correlate with breaks in slope of the channels (or knick points) such that the high gradient indices (K) with values between 2,000-3,000 and higher than 3,000 suggest that incision is controlled by tectonic activity. Our analysis reveals that many of the ranges of the Western Cordillera were uplifted to the actual elevations where peaks reach to 6,000 m above sea level by thrusting along steeply dipping faults. We correlate this uplift with the Quechua Phase of Neogene age documented for the Subandean thrust belt. The rivers of the Amazonas Basin have steep slopes and high gradient indices of 2,000-3,000 and locally more than 3,000 in those segments where the rivers flow over the crystalline basement of the Eastern Cordillera affected by vertical faulting. Gradient indices decrease to 1,000-2,000 within the east-vergent thrust belt of the Subandean Zone. Here a correlation between breaks in river channel slopes and location of thrust faults can be established, suggesting that the young, Quechua Phase thrust faults of the Subandean thrust belt, which involve Neogene sediments, influenced the channel geometry. In the eastern lowlands, these rivers become meandering and flow parallel to anticlines that formed in the hanging wall of Quechua Phase thrust faults, suggesting that the river courses were actively displaced outward into the foreland.

  7. Two new species of Siphocampylus (Campanulaceae, Lobelioideae) from the Central Andes

    PubMed Central

    Lagomarsino, Laura P.; Santamaría-Aguilar, Daniel

    2016-01-01

    Abstract Two species of Siphocampylus (Campanulaceae: Lobelioideae) from the Central Andes of Peru and Bolivia are described, illustrated, and discussed with reference to related species. One species, Siphocampylus antonellii, is endemic to high elevation grasslands of Calca, Peru, while the second, Siphocampylus siberiensis, is endemic to cloud forests of Cochabamba, Bolivia. Both species are robust shrubs that produce tubular pink flowers that are likely pollinated by hummingbirds. PMID:26884710

  8. Miocene orographic uplift forces rapid hydrological change in the southern central Andes

    PubMed Central

    Rohrmann, Alexander; Sachse, Dirk; Mulch, Andreas; Pingel, Heiko; Tofelde, Stefanie; Alonso, Ricardo N.; Strecker, Manfred R.

    2016-01-01

    Rainfall in the central Andes associated with the South American Monsoon and the South American Low-Level Jet results from orographic effects on atmospheric circulation exerted by the Andean Plateau and the Eastern Cordillera. However, despite its importance for South American climate, no reliable records exist that allow decoding the evolution of thresholds and interactions between Andean topography and atmospheric circulation, especially regarding the onset of humid conditions in the inherently dry southern central Andes. Here, we employ multi-proxy isotope data of lipid biomarkers, pedogenic carbonates and volcanic glass from the Eastern Cordillera of NW Argentina and present the first long-term evapotranspiration record. We find that regional eco-hydrology and vegetation changes are associated with initiation of moisture transport via the South American Low-Level Jet at 7.6 Ma, and subsequent lateral growth of the orogen at 6.5 Ma. Our results highlight that topographically induced changes in atmospheric circulation patterns, not global climate change, were responsible for late Miocene environmental change in this part of the southern hemisphere. This suggests that mountain building over time fundamentally controlled habitat evolution along the central Andes. PMID:27767043

  9. The growth of the central Andes 22-26°S (Invited)

    NASA Astrophysics Data System (ADS)

    Quade, J.; DeCelles, P. G.; Carrapa, B.; Murray, K. E.; Canavan, R. R.; Huntington, K. W.; Gehrels, G. E.

    2013-12-01

    In this talk we synthesize geologic observations with new isotopic evidence for the timing and magnitude of uplift for the central Andes between 22-26°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 first, 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 to > 3 km by no later than 15 Ma. The proximal portions of the Paleogene foreland basin system were uplifted and hydrographically isolated from easterly moisture sources, promoting the precipitation of evaporites. In the third orogenic stage during the Plio-Pleistocene, Andean deformation accelerated and stepped eastward to form the modern Subandes, accounting for the final ~15-20% of the current cross-section of the Andes. About 0.5 km of elevation was added unevenly to the Western Cordillera and Puna 10-2 Ma by voluminous volcanism. The two largest episodes of uplift and eastward propagation of the orogenic front and of the foreland flexural wave, ~50 (?)-40 and <5 Ma, overlap with or immediately post-date periods of very rapid plate convergence, high flux magmatism in the magmatic arc, and crustal thickening. Uplift does not correlate with an hypothesized mantle lithospheric foundering event in the early Oligocene. Development of hyperaridity in the Atacama Desert by the mid-Miocene post-dates the two-step elevation gain to >3 km of most (~75%) of the Andes. Hence, the record suggests that hyperarid

  10. Facing unprecedented drying of the Central Andes? Precipitation variability over the period AD 1000-2100

    NASA Astrophysics Data System (ADS)

    Neukom, Raphael; Rohrer, Mario; Calanca, Pierluigi; Salzmann, Nadine; Huggel, Christian; Acuña, Delia; Christie, Duncan A.; Morales, Mariano S.

    2015-08-01

    Projected future trends in water availability are associated with large uncertainties in many regions of the globe. In mountain areas with complex topography, climate models have often limited capabilities to adequately simulate the precipitation variability on small spatial scales. Also, their validation is hampered by typically very low station density. In the Central Andes of South America, a semi-arid high-mountain region with strong seasonality, zonal wind in the upper troposphere is a good proxy for interannual precipitation variability. Here, we combine instrumental measurements, reanalysis and paleoclimate data, and a 57-member ensemble of CMIP5 model simulations to assess changes in Central Andes precipitation over the period AD 1000-2100. This new database allows us to put future projections of precipitation into a previously missing multi-centennial and pre-industrial context. Our results confirm the relationship between regional summer precipitation and 200 hPa zonal wind in the Central Andes, with stronger Westerly winds leading to decreased precipitation. The period of instrumental coverage (1965-2010) is slightly dryer compared to pre-industrial times as represented by control simulations, simulations from the past Millennium, ice core data from Quelccaya ice cap and a tree-ring based precipitation reconstruction. The model ensemble identifies a clear reduction in precipitation already in the early 21st century: the 10 year running mean model uncertainty range (ensemble 16-84% spread) is continuously above the pre-industrial mean after AD 2023 (AD 2028) until the end of the 21st century in the RCP2.6 (RCP8.5) emission scenario. Average precipitation over AD 2071-2100 is outside the range of natural pre-industrial variability in 47 of the 57 model simulations for both emission scenarios. The ensemble median fraction of dry years (defined by the 5th percentile in pre-industrial conditions) is projected to increase by a factor of 4 until 2071-2100 in

  11. Lower bound on the amount of crustal shortening in the central Bolivia Andes

    SciTech Connect

    Sheffels, B.M. )

    1990-09-01

    Balanced cross sections across the Cordillera Oriental and Subandean zone of the central Bolivian Andes indicate that crustal shortening probably has played the dominant role in orogeny in this convergent margin setting. A minimum amount of shortening, 210 km, is documented, which can account for two-thirds of the present-day crustal cross-sectional area along a transect spanning the entire mountain range. Substantial crustal shortening may also require loss of the lower lithosphere to the asthenosphere. A large, minimum amount of crustal shortening in the Bolivian Andes shows, contrary to common assumptions about orogeny, that (1) magmatic addition may be volumetrically less important in orogeny in Andean-type margins and (2) crustal shortening is not uniquely associated with continental or island-arc collision.

  12. The Pampean flat-slab of the Central Andes

    NASA Astrophysics Data System (ADS)

    Ramos, Victor A.; Cristallini, E. O.; Pérez, Daniel J.

    2002-04-01

    Late Cenozoic Andean deformation in the Pampean segment of Argentina and Chile (27°00'-33°30'S) provides an exceptional opportunity to study the orogenic effects of flat subduction in an active convergent margin. At these latitudes, constraints derived from oceanic geomorphic structures indicate that collision of the Juan Fernandez Ridge in the Nazca plate with the Chilean trench propagated from north to south from ca. 18 to ca. 11 Ma. In this region, Cenozoic tectonics have resulted in the development of the Principal and Frontal Cordilleras, the Cuyo Precordillera, and the associated Sierras Pampeanas in the eastward foreland region. The analyses of different structural transects across the Sierras Pampeanas between 27 and 33°S latitudes show a southward diachronic beginning of basement block uplift from 7.6 to 6 Ma in the Sierra de Aconquija (27°S), 4.5 to 4.19 Ma at Sierra de Famatina (29°S), 5.5 to 4.7 Ma at Sierra de Pocho (31°S), and ca. 2.6 Ma at Sierra de San Luis (33°S). Uplift times are constrained by the age of synorogenic deposits, fission-track data on apatite, and hydrogen isotopes in alunite, where available. These time constraints are compared with the migration and expansion of the magmatic activity into the foreland. The relation of these two data sets shows a striking coincidence, after a residence time of approximately 4-2.6 Ma, between magmatic activity and failure of the crust that resulted in basement block uplift. Thermal weakening of the crust associated with eastward migration of arc magmatism acted to elevate brittle-ductile subsurface décollments, thus leading to thick-skinned basement uplift of the Sierras Pampeanas. The evolution of the Sierras Pampeanas is linked to that of the main Andes at 33°S latitude. The main deformation phases and uplift of the thin- and thick-skinned fold and thrust belts of Principal Cordillera occurred between 20 and 8.6 Ma. Arc volcanism migrated eastward at this latitude between 16 and 15.8 Ma

  13. The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes

    PubMed Central

    Goss, Erica M.; Tabima, Javier F.; Cooke, David E. L.; Restrepo, Silvia; Fry, William E.; Forbes, Gregory A.; Fieland, Valerie J.; Cardenas, Martha; Grünwald, Niklaus J.

    2014-01-01

    Phytophthora infestans is a destructive plant pathogen best known for causing the disease that triggered the Irish potato famine and remains the most costly potato pathogen to manage worldwide. Identification of P. infestan’s elusive center of origin is critical to understanding the mechanisms of repeated global emergence of this pathogen. There are two competing theories, placing the origin in either South America or in central Mexico, both of which are centers of diversity of Solanum host plants. To test these competing hypotheses, we conducted detailed phylogeographic and approximate Bayesian computation analyses, which are suitable approaches to unraveling complex demographic histories. Our analyses used microsatellite markers and sequences of four nuclear genes sampled from populations in the Andes, Mexico, and elsewhere. To infer the ancestral state, we included the closest known relatives Phytophthora phaseoli, Phytophthora mirabilis, and Phytophthora ipomoeae, as well as the interspecific hybrid Phytophthora andina. We did not find support for an Andean origin of P. infestans; rather, the sequence data suggest a Mexican origin. Our findings support the hypothesis that populations found in the Andes are descendants of the Mexican populations and reconcile previous findings of ancestral variation in the Andes. Although centers of origin are well documented as centers of evolution and diversity for numerous crop plants, the number of plant pathogens with a known geographic origin are limited. This work has important implications for our understanding of the coevolution of hosts and pathogens, as well as the harnessing of plant disease resistance to manage late blight. PMID:24889615

  14. Human impacts on headwater fluvial systems in the northern and central Andes

    NASA Astrophysics Data System (ADS)

    Harden, Carol P.

    2006-09-01

    South America delivers more freshwater runoff to the ocean per km 2 land area than any other continent, and much of that water enters the fluvial system from headwaters in the Andes Mountains. This paper reviews ways in which human occupation of high mountain landscapes in the Andes have affected the delivery of water and sediment to headwater river channels at local to regional scales for millennia, and provides special focus on the vulnerability of páramo soils to human impact. People have intentionally altered the fluvial system by damming rivers at a few strategic locations, and more widely by withdrawing surface water, primarily for irrigation. Unintended changes brought about by human activities are even more widespread and include forest clearance, agriculture, grazing, road construction, and urbanization, which increase rates of rainfall runoff and accelerate processes of water erosion. Some excavations deliver more sediment to river channels by destabilizing slopes and triggering processes of mass-movement. The northern and central Andes are more affected by human activity than most high mountain regions. The wetter northern Andes are also unusual for the very high water retention characteristics of páramo (high elevation grass and shrub) soils, which cover most of the land above 3000 m. Páramo soils are important regulators of headwater hydrology, but human activities that promote vegetation loss and drying cause them to lose water storage capacity. New data from a case study in southern Ecuador show very low bulk densities (median 0.26 g cm - 3 ), high organic matter contents (median 43%), and high water-holding capacities (12% to 86% volumetrically). These data document wetter soils under grass than under tree cover. Effects of human activity on the fluvial system are evident at local scales, but difficult to discern at broader scales in the regional context of geomorphic adjustment to tectonic and volcanic processes.

  15. Climate in the Western Cordillera of the Central Andes over the last 4300 years

    NASA Astrophysics Data System (ADS)

    Engel, Zbyněk; Skrzypek, Grzegorz; Chuman, Tomáš; Šefrna, Luděk; Mihaljevič, Martin

    2014-09-01

    The Distichia peat core obtained in the Carhuasanta valley near Nevado Mismi, Cordillera Chila, provides information on climatic and environmental conditions over the last ˜4300 years. The relative changes in the stable carbon isotope composition of plant remains preserved in the core reflect major temperature fluctuations in the Western Cordillera of the southern Peruvian Andes. These temperature variations can be additionally linked with the changes in precipitation patterns by analysing C% and C/N ratio in the core. Relatively warm and moist conditions prevailed from 4280 to 3040 cal. yrs BP (BC 2330-1090) with a short colder dry episode around 3850 cal. yrs BP (BC 1900). The most prominent climate changes recorded in the peat occurred between 3040 and 2750 cal. yrs BP (BC 1090-800) when the initial warming turned to a rapid cooling to temperatures at least 2 °C lower than the mean for the Late Holocene. Initially drier conditions within this event turned to a short wet phase after 2780 cal. yrs BP (BC 830) when the temperature increased again. This event coincides with significant changes in peat and ice core records in the Central Andes matching the timing of the global climate event around 2.8 cal. ka BP. Climatic conditions in the study area became relatively dry and stable after the event for about 800 years. Highly variable temperatures and humidity prevailed during the last 2000 years when an extended warm and relatively humid period occurred between 640 and 155 cal. yrs BP (AD 1310-1795) followed by predominantly colder and drier conditions. The established δ13C peat record represents the first continuous proxy for the temperature in the southern Peruvian Andes dated by the AMS 14C. Distichia peat is wide spread in the Andes and the proposed approach can be applied elsewhere in high altitudes, where no other traditional climate proxies are available.

  16. Ages and potential drivers of fluvial fill terrace formation in the southern-central Andes, NW Argentina

    NASA Astrophysics Data System (ADS)

    Tofelde, S.; Savi, S.; Wickert, A. D.; Wittmann, H.; Alonso, R. N.; Strecker, M. R.; Schildgen, T. F.

    2015-12-01

    Fluvial fill terraces record changes in past sediment to water discharge ratios. Across the world, fill terrace formation in glaciated catchments has been linked to variable sediment production and river discharge over glacial-interglacial cycles. However, pronounced fill terraces far from major glaciers and ice sheets have the potential to record a different set of climate forcings. So far, little is known about how changes in global climate on multi-millenial timescales affected the rainfall patterns in the interior of South America, or how those changes might be reflected in the landscape. Nonetheless, several studies in the Central Andes have linked terrace formation to precessionally-controlled changes in precipitation. In this study, we investigate the timing of fluvial fill terrace planation and abandonment in the Quebrada del Toro, an intermontane basin located in the Eastern Cordillera of the southern-central Andes in NW Argentina. Fluvial fills in the valley reach more than 100 m above the current river level. Within the fills, we observe a minimum of 5 terrace levels with pronounced differences in their extent and preservation. These fills document successive episodes of incision, punctuated by periods of lateral planation and possible partial re-filling. The filling and re-incision has previously been associated with tectonic activity in the basin, but the potential superposed role of climate cycles in forming terraces has not been considered. We sampled four CRN (10Be) depth profiles to date the abandonment of the broadest terrace surfaces, least affected by later overwash and erosion. The ages fall within the late Pleistocene (~ 80 ka to 400 ka). While the presence of inflationary soils beneath desert pavements make precise age determinations difficult, our preliminary calculations suggest a potential link to orbital eccentricity (~100 kyr) cycles, pointing to a different timescale of landscape response to climate forcing compared to previous studies.

  17. On Restoring Sedimentary Basins for Post-Depositional Deformation - Paleozoic Basins of the Central Andes

    NASA Astrophysics Data System (ADS)

    Bahlburg, H.

    2015-12-01

    The reconstruction and interpretation of sedimentary basins incorporated into folded and thrusted mountain belts is strongly limited by the style and intensity of shortening. This problem is exacerbated if deformation is polyphasic as is the case for the Paleozoic basins in the central Andes. Some of these have been deformed by folding and thrusting during at least 3 events in the Late Ordovician, the Late Paleozoic and Cenozoic. A realistic reconstruction of the original basin dimensions and geometries from outcrops and maps appears to be almost impossible. We present results of a stepwise reconstruction of the Paleozoic basins of the central Andes by restoring basin areas and fills accounting for crustal shortening. The structurally most prominent feature of the central Andes is the Bolivian Orocline which accomodated shortening in the last 45 Ma on the order of between 300 and 500 km. In a first step basins were restored by accounting for Cenozoic rotation and shortening by deconvolving the basins using an enhanced version of the oroclinal bending model of Ariagada et al. (2008). Results were then restored stepwise for older deformation. Constraints on these subsequent steps are significantly poorer as values of shortening can be derived only from folds and thusts apparent in outcrops. The amount of shortening accomodated on unexposed and therefore unknown thrusts can not be quantified and is a significant source of error very likely leading to an underestimation of the amount of shortening. Accepting these limitations, basin restoration results in an increase in basin area by ≥100%. The volumes of stratigraphically controlled basin fills can now be redistributed over the wider, restored area, translating into smaller rates of accumulation and hence required subsidence. The restored rates conform to those of equivalent modern basin settings and permit a more realistic and actualistic analysis of subsidence drivers and the respective tectonic framework.

  18. Lithosphere Removal in the Central Andes: Reconciling Seismic Images and Elevation History

    NASA Astrophysics Data System (ADS)

    Henderson, O.; Currie, C. A.

    2015-12-01

    Shortening of the upper crust should be accompanied by thickening of the deeper lithosphere. However, for many orogens, including the central Andes, geophysical and geological observations indicate that mantle lithosphere is spatially heterogeneous, being anomalously thin or absent. Seismic studies of the central Andes suggest that mantle lithosphere is locally removed. Also, present day elevations of the central Andean Plateau have been explained by rapid removal of mantle lithosphere over the last 10 Ma. Yet, the geological record is innately incomplete, and seismic tomography and receiver functions can offer only a present day snapshot of the subsurface. None of these techniques provides concrete insight into the physical processes responsible for current Andean elevations (3-5 km). A 2D plane-strain thermo-mechanical code, SOPALE, is used to examine the deep lithospheric dynamics connected to mantle lithosphere removal within a subduction zone setting, such as the Andes. Three models have been tested: removal by viscous dripping, by delamination, and a model with no removal. The removal models contain a high density eclogite root, creating a contrast between mantle lithosphere and mantle material. For the viscous drip models, mantle lithosphere is removed within 2.5-5 Myrs, descending subvertically through the mantle, causing subsequent surface rebound. Prior to this rebound, surface topography subsides locally over the dense root. This subsidence is influenced by crustal rheology, where weaker crustal rheologies produce deep, narrower basins (25-75 km wide, ~1 km deep), and stronger crustal rheologies produce shallow, broader basins (300-400 km wide, ~0.5 km deep). Delamination, which involves the coherent removal of mantle lithosphere along the Moho, affects a larger region, and is reflected in broader basins that extend into the back-arc. In all models, the deep lithosphere dynamics have an appreciable effect on surface topography, therefore, removal events

  19. Prediction of extreme floods in the Central Andes by means of Complex Networks

    NASA Astrophysics Data System (ADS)

    Boers, Niklas; Bookhagen, Bodo; Barbosa, Henrique; Marwan, Norbert; Kurths, Jürgen; Marengo, Jose

    2014-05-01

    Based on a non-linear synchronisation measure and complex network theory, we present a novel framework for the prediction of extreme events of spatially embedded, interrelated time series. This method is general in the sense that it can be applied to any type of spatially sampled time series with significant interrelations, ranging from climate observables to biological or stock market data. In this presentation, we apply our method to extreme rainfall in South America and show how this leads to the prediction of more than 60% (90% during El Niño conditions) of extreme rainfall events in the eastern Central Andes of Bolivia and northern Argentina, with only 1% false alarms. From paleoclimatic to decadal time scales, the Central Andes continue to be subject to pronounced changes in climatic conditions. In particular, our and past work shows that frequency as well as magnitudes of extreme rainfall events have increased significantly during past decades, calling for a better understanding of the involved climatic mechanisms. Due to their large spatial extend and occurrence at high elevations, these extreme events often lead to severe floods and landslides with disastrous socioeconomic impacts. They regularly affect tens of thousands of people and produce estimated costs of the order of several hundred million USD. Alongside with the societal value of predicting natural hazards, our study provides insights into the responsible climatic features and suggests interactions between Rossby waves in polar regions and large scale (sub-)tropical moisture transport as a driver of subseasonal variability of the South American monsoon system. Predictable extreme events result from the propagation of extreme rainfall from the region of Buenos Aires towards the Central Andes given characteristic atmospheric conditions. Our results indicate that the role of frontal systems originating from Rossby waves in polar latitudes is much more dominant for controlling extreme rainfall in

  20. Simulations of the future precipitation climate of the Central Andes using a coupled regional climate model

    NASA Astrophysics Data System (ADS)

    Nicholls, S.; Mohr, K. I.

    2014-12-01

    The meridional extent and complex orography of the South American continent contributes to a wide diversity of climate regimes ranging from hyper-arid deserts to tropical rainforests to sub-polar highland regions. Global climate models, although capable of resolving synoptic-scale South American climate features, are inadequate for fully-resolving the strong gradients between climate regimes and the complex orography which define the Tropical Andes given their low spatial and temporal resolution. Recent computational advances now make practical regional climate modeling with prognostic mesoscale atmosphere-ocean coupled models, such as the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system, to climate research. Previous work has shown COAWST to reasonably simulate the both the entire 2003-2004 wet season (Dec-Feb) as validated against both satellite and model analysis data. More recently, COAWST simulations have also been shown to sensibly reproduce the entire annual cycle of rainfall (Oct 2003 - Oct 2004) with historical climate model input. Using future global climate model input for COAWST, the present work involves year-long cycle spanning October to October for the years 2031, 2059, and 2087 assuming the most likely regional climate pathway (RCP): RCP 6.0. COAWST output is used to investigate how global climate change impacts the spatial distribution, precipitation rates, and diurnal cycle of precipitation patterns in the Central Andes vary in these yearly "snapshots". Initial results show little change to precipitation coverage or its diurnal cycle, however precipitation amounts did tend drier over the Brazilian Plateau and wetter over the Western Amazon and Central Andes. These results suggest potential adjustments to large-scale climate features (such as the Bolivian High).

  1. Multiethnicity, pluralism, and migration in the south central Andes: An alternate path to state expansion

    PubMed Central

    Goldstein, Paul S.

    2015-01-01

    The south central Andes is known as a region of enduring multiethnic diversity, yet it is also the cradle of one the South America’s first successful expansive-state societies. Social structures that encouraged the maintenance of separate identities among coexistent ethnic groups may explain this apparent contradiction. Although the early expansion of the Tiwanaku state (A.D. 600–1000) is often interpreted according to a centralized model derived from Old World precedents, recent archaeological research suggests a reappraisal of the socio-political organization of Tiwanaku civilization, both for the diversity of social entities within its core region and for the multiple agencies behind its wider program of agropastoral colonization. Tiwanaku’s sociopolitical pluralism in both its homeland and colonies tempers some of archaeology’s global assumptions about the predominant role of centralized institutions in archaic states. PMID:26195732

  2. Bird conservation would complement landslide prevention in the Central Andes of Colombia.

    PubMed

    Ocampo-Peñuela, Natalia; Pimm, Stuart L

    2015-01-01

    Conservation and restoration priorities often focus on separate ecosystem problems. Inspired by the November 11th (2011) landslide event near Manizales, and the current poor results of Colombia's Article 111 of Law 99 of 1993 as a conservation measure in this country, we set out to prioritize conservation and restoration areas where landslide prevention would complement bird conservation in the Central Andes. This area is one of the most biodiverse places on Earth, but also one of the most threatened. Using the case of the Rio Blanco Reserve, near Manizales, we identified areas for conservation where endemic and small-range bird diversity was high, and where landslide risk was also high. We further prioritized restoration areas by overlapping these conservation priorities with a forest cover map. Restoring forests in bare areas of high landslide risk and important bird diversity yields benefits for both biodiversity and people. We developed a simple landslide susceptibility model using slope, forest cover, aspect, and stream proximity. Using publicly available bird range maps, refined by elevation, we mapped concentrations of endemic and small-range bird species. We identified 1.54 km(2) of potential restoration areas in the Rio Blanco Reserve, and 886 km(2) in the Central Andes region. By prioritizing these areas, we facilitate the application of Article 111 which requires local and regional governments to invest in land purchases for the conservation of watersheds.

  3. Bird conservation would complement landslide prevention in the Central Andes of Colombia.

    PubMed

    Ocampo-Peñuela, Natalia; Pimm, Stuart L

    2015-01-01

    Conservation and restoration priorities often focus on separate ecosystem problems. Inspired by the November 11th (2011) landslide event near Manizales, and the current poor results of Colombia's Article 111 of Law 99 of 1993 as a conservation measure in this country, we set out to prioritize conservation and restoration areas where landslide prevention would complement bird conservation in the Central Andes. This area is one of the most biodiverse places on Earth, but also one of the most threatened. Using the case of the Rio Blanco Reserve, near Manizales, we identified areas for conservation where endemic and small-range bird diversity was high, and where landslide risk was also high. We further prioritized restoration areas by overlapping these conservation priorities with a forest cover map. Restoring forests in bare areas of high landslide risk and important bird diversity yields benefits for both biodiversity and people. We developed a simple landslide susceptibility model using slope, forest cover, aspect, and stream proximity. Using publicly available bird range maps, refined by elevation, we mapped concentrations of endemic and small-range bird species. We identified 1.54 km(2) of potential restoration areas in the Rio Blanco Reserve, and 886 km(2) in the Central Andes region. By prioritizing these areas, we facilitate the application of Article 111 which requires local and regional governments to invest in land purchases for the conservation of watersheds. PMID:25737819

  4. Bird conservation would complement landslide prevention in the Central Andes of Colombia

    PubMed Central

    Ocampo-Peñuela, Natalia

    2015-01-01

    Conservation and restoration priorities often focus on separate ecosystem problems. Inspired by the November 11th (2011) landslide event near Manizales, and the current poor results of Colombia’s Article 111 of Law 99 of 1993 as a conservation measure in this country, we set out to prioritize conservation and restoration areas where landslide prevention would complement bird conservation in the Central Andes. This area is one of the most biodiverse places on Earth, but also one of the most threatened. Using the case of the Rio Blanco Reserve, near Manizales, we identified areas for conservation where endemic and small-range bird diversity was high, and where landslide risk was also high. We further prioritized restoration areas by overlapping these conservation priorities with a forest cover map. Restoring forests in bare areas of high landslide risk and important bird diversity yields benefits for both biodiversity and people. We developed a simple landslide susceptibility model using slope, forest cover, aspect, and stream proximity. Using publicly available bird range maps, refined by elevation, we mapped concentrations of endemic and small-range bird species. We identified 1.54 km2 of potential restoration areas in the Rio Blanco Reserve, and 886 km2 in the Central Andes region. By prioritizing these areas, we facilitate the application of Article 111 which requires local and regional governments to invest in land purchases for the conservation of watersheds. PMID:25737819

  5. The Bolivian Orocline and its implications for the origin of the central Andes

    NASA Astrophysics Data System (ADS)

    Arriagada, C.

    2015-12-01

    The tectonic evolution of the Central Andes includes a complex combination of thrusting, wrenching and block rotation leading progressively to the curvature of the orogenic system of the South American continental margin at 18ºS (Bolivian Orocline). Tectonic deformation in the Bolivian Orocline cannot be realistically restored using information from balanced cross sections alone, as the deformation includes an important component of block rotation, associated to counterclockwise block rotation in southern Peru and clockwise rotation in northern Chile. Recent work shows that block rotations in the forearc are essentially pre-early Miocene, predating the onset of Neogene shortening in the Sub Andean zone. Most rotations in the forearc of northern Chile where acquired through a single tectonic event during the Paleogene-early Miocene which probably coincides with the Eocene orogen-wide Incaic event which affected large regions of the central Andes between ca. 50 and 40 Ma. Results from 2D restoration experiments support the hypothesis of the Paleogene formation of the Bolivian Orocline, as a consequence of differential shortening, concentrated in the Eastern Cordillera of Bolivia, southern Peru and northwestern Argentina. Within the southern central Andes four additional curvatures including striking changes in the pattern of rotations have been discovered. From north to south these are the Antofagasta-Calama Lineament, Vallenar, Maipo and Arauco oroclines. However, an important part of rotation needs to be balanced, in the forearc region, by two major conjugate oblique shear zones (Abancay Deflection and Antofagasta-Calama Lineament). These structural features are probably related to inherited lithospheric discontinuities associated with the accretion of basement terranes which could be responsible for producing and delimitating significant and abrupt changes in the magnitude of the Central Andean Rotation Pattern along the margin. While shortening and crustal

  6. Influence of spatial resolution on precipitation simulations for the central Andes Mountains

    NASA Astrophysics Data System (ADS)

    Trachte, Katja; Bendix, Jörg

    2013-04-01

    The climate of South America is highly influenced by the north-south oriented Andes Mountains. Their complex structure causes modifications of large-scale atmospheric circulations resulting in various mesoscale phenomena as well as a high variability in the local conditions. Due to their height and length the terrain generates distinctly climate conditions between the western and the eastern slopes. While in the tropical regions along the western flanks the conditions are cold and arid, the eastern slopes are dominated by warm-moist and rainy air coming from the Amazon basin. Below 35° S the situation reverses with rather semiarid conditions in the eastern part and temperate rainy climate along southern Chile. Generally, global circulation models (GCMs) describe the state of the global climate and its changes, but are disabled to capture regional or even local features due to their coarse resolution. This is particularly true in heterogeneous regions such as the Andes Mountains, where local driving features, e. g. local circulation systems, highly varies on small scales and thus, lead to a high variability of rainfall distributions. An appropriate technique to overcome this problem and to gain regional and local scale rainfall information is the dynamical downscaling of the global data using a regional climate model (RCM). The poster presents results of the evaluation of the performance of the Weather Research and Forecasting (WRF) model over South America with special focus on the central Andes Mountains of Ecuador. A sensitivity study regarding the cumulus parametrization, microphysics, boundary layer processes and the radiation budget is conducted. With 17 simulations consisting of 16 parametrization scheme combinations and 1 default run a suitable model set-up for climate research in this region is supposed to be evaluated. The simulations were conducted in a two-way nested mode i) to examine the best physics scheme combination for the target and ii) to

  7. The Glacier Inventory of the Central Andes of Argentina (31°-35°S)

    NASA Astrophysics Data System (ADS)

    Ferri Hidalgo, L.; Zalazar, L.; Castro, M.; Pitte, P.; Masiokas, M. H.; Ruiz, L.; Villalba, R.; Delgado, S.; Gimenez, M.; Gargantini, H.

    2015-12-01

    The National Law for protection of glaciers in Argentina envisages the development of a National Inventory of Glaciers. All glaciers and periglacial landforms which are important as strategic water resource must be properly identified and mapped. Here we present a detailed and complete glacier and rock glacier inventory of the Central Andes of Argentina between 31° and 35°S. This semi-arid region contains some of the highest mountains of South America and concentrates the second most glacierized area in Argentina after the Patagonian Andes. To develop the inventory, we used remotely sensed data and related techniques complemented with field surveys. Clean ice and perennial snowfields were identified applying an automatic extraction method on medium spatial-resolution images. Debris-covered and rock glaciers were manually digitized on higher spatial-resolution images. With minor modifications, the present digital inventory is consistent with GLIMS standards. For each glacier, we derived 38 database fields, adding five specific attributes for rock glaciers, which are not included in the original GLIMS database. In total we identified 8069 glaciers covering an area of 1768 km2. Debris-covered ice and rock glaciers represent 57% of the total inventoried area. In this region, rock glaciers are a common feature in the arid landscape and constitute an important water reserve at regional scale. Many glaciers were characterized by gradual transition from debris-covered glaciers, in the upper part, to rock glaciers, in the lower sector. The remaining 43% includes clean ice glaciers and permanent snowfields. These are mostly mountain and valley-type glaciers with medium-to-small sizes. This detailed inventory constitutes a valuable contribution to the ongoing global efforts (e.g. WGI, RGI and GLIMS) to map the world's glaciers. It is also the base for ongoing glaciological, climatological and hydrological studies in this portion of southern Andes.

  8. Climate Change Driven Implications on Spatial Distribution of High Andean Peatlands in the Central Andes

    NASA Astrophysics Data System (ADS)

    Otto, Marco; Gibbons, Richard E.

    2013-04-01

    High Andean peatlands are among the most unique habitats in the tropical Andes and certainly among the least studied. High Andean peatlands occur patchily in montane grassland and scrub below snow line and above tree line. These high-elevation peatlands are sustained by glacial runoff and seasonal precipitation. We used remote sensing data to estimate that peatland habitat is approximately 2.5 % of our study region in the Puna, an ecoregion located in the high Andes above 4000 m a.s.l. Individual sizes of our estimated peatland polygons ranged from 0.72 ha to 1079 ha with a mean size of 4.9 ha. Climate change driven implications on spatial distribution of high Andean peatlands were assessed in two ways. First, we estimated the effect of predicted regional temperature increase by using the standard lapse rate of 2° C per 300 m for assessing peatland habitat patches that would remain above a critical thermocline. Nearly 80% of peatland habitat patches were predicted to occur below the thermocline if the prediction of 4° C temperature increase is realized. The second assessment relied on the quantified assumption that permanent snow or glacier cover, topographic characteristics (e.g. slope) and precipitation of a basin are essential variables in the occurrence of high Andean peatlands. All 17 basins were predicted to have a decrease in peatland habitat due to snow line uplift, decrease in precipitation and consequent insufficient wetland inflows. Total habitat loss was predicted for two basins in the semi-arid part of the study area with a snow line uplift to 5600 m and a projected decrease in precipitation of 1 mm per year over the next 40 years. A combined result of both assessments provides important information on climate change driven implications on the hydrology of high Andean peatlands and potential consequences for their spatial distribution within the Central Andes.

  9. Intraseasonal variability of organized convective systems in the Central Andes: Relationship to Regional Dynamical Features

    NASA Astrophysics Data System (ADS)

    Mohr, K. I.; Slayback, D. A.; Nicholls, S.; Yager, K.

    2013-12-01

    The Andes extend from the west coast of Colombia (10N) to the southern tip of Chile (53S). In southern Peru and Bolivia, the Central Andes is split into separate eastern and western cordilleras, with a high plateau (≥ 3000 m), the Altiplano, between them. Because 90% of the Earth's tropical mountain glaciers are located in the Central Andes, our study focuses on this region, defining its zonal extent as 7S-21S and the meridional extent as the terrain 1000 m and greater. Although intense convection occurs during the wet season in the Altiplano, it is not included in the lists of regions with frequent or the most intense convection. The scarcity of in-situ observations with sufficient density and temporal resolution to resolve individual storms or even mesoscale-organized cloud systems and documented biases in microwave-based rainfall products in poorly gauged mountainous regions have impeded the development of an extensive literature on convection and convective systems in this region. With the tropical glaciers receding at unprecedented rates, leaving seasonal precipitation as an increasingly important input to the water balance in alpine valley ecosystems and streams, understanding the nature and characteristics of the seasonal precipitation becomes increasingly important for the rural economies in this region. Previous work in analyzing precipitation in the Central Andes has emphasized interannual variability with respect to ENSO, this is the first study to focus on shorter scale variability with respect to organized convection. The present study took advantage of the University of Utah's Precipitation Features database compiled from 14 years of TRMM observations (1998-2012), supplemented by field observations of rainfall and streamflow, historical gauge data, and long-term WRF-simulations, to analyze the intraseasonal variability of precipitating systems and their relationship regional dynamical features such as the Bolivian High. Through time series and

  10. What controls millennial-scale denudation rates across the Central Andes?

    NASA Astrophysics Data System (ADS)

    Zeilinger, Gerold; Korup, Oliver; Schlunegger, Fritz; Kober, Florian

    2015-04-01

    Sustainable planning of erosion control measures in the Central Andes requires robust knowledge about natural denudation rates. We explore a large dataset combining new and published 10Be (and 26Al) catchment-wide denudation rates from a swath at 17 to 19° S spanning the Western Cordillera that rises from sea level to 5500 m elevation; the Altiplano at ~4000 m; the Eastern Cordillera with elevations up to 6500 m; the Interandean Zone; the Subandean Zone; and the Chaco Plain at 300 m. The selected catchments span a large spread regarding morphometric and climate properties where mean slope angles range from 1 to 31°, and mean precipitation from 100 to 3900 mm/a. The denudation rates (0.0036 to 1.93 mm/a) are averaged over millennia, and reveal two to three magnitudes difference across the Central Andes. The regional distribution of denudation rates clearly demonstrates a more complex interaction of geomorphological, geological and meteorological parameters with the dominant geomorphological processes. In order to elucidate the key controls on denudation, we use multivariate statistics such as principal component analysis in order to remove potentially redundant predictors of denudation in the studied catchments. These predictors include catchment elevation, topographic relief, hillslope inclination, mean precipitation, tree cover, specific stream power, channel steepness indices, sinuosity, drainage density and hypsometric index that we derived from the SRTM 90 m Digital Elevation Database, the Tropical Rainfall Measuring Mission (TRMM) data, and the Terra MODIS Vegetation Continuous Fields dataset. Additionally, the rock strength index (PLI) was estimated based on geological units. Preliminary results allow distinguishing five different longitudinal domains of denudation on the basis of climatic regime, hillslope steepness, and the degree of accumulated crustal deformation. We find that the pattern of 10Be catchment-wide denudation rates in the Central Andes

  11. The Loncopué Trough: A Cenozoic basin produced by extension in the southern Central Andes

    NASA Astrophysics Data System (ADS)

    Folguera, Andrés; Rojas Vera, Emilio; Bottesi, Germán; Zamora Valcarce, Gonzalo; Ramos, Victor A.

    2010-05-01

    The Loncopué Trough is located in the hinterland Andean zone between 36°30' and 39°S. It constitutes a topographic low bounded by normal faults and filled by lavas and sediments less than 5 Ma old. Reprocessed seismic lines show wedge-like depocenters up to 1700 m deep associated with high-angle faults, correlated with the 27-17 Ma Cura Mallín basin deposits, and buried beneath Pliocene to Quaternary successions and Late Miocene foreland sequences. The southern Central Andes seem to have been under extension in the hinterland zone some 27 Ma ago and again at approximately 5 Ma ago. This last extensional period could have been the product of slab steepening after a shallow subduction cycle in the area, although other alternatives are discussed. Orogenic wedge topography, altered by the first extensional stage in the area, was recovered through Late Miocene inversion, and was associated with foreland sequences. However, since the last extension (<5 Ma) the Andes have not recovered their characteristic contractional behavior that controlled past orogenic growth.

  12. Altitudinal variation in fish assemblage diversity in streams of the central Andes of Colombia.

    PubMed

    Jaramillo-Villa, U; Maldonado-Ocampo, J A; Escobar, F

    2010-06-01

    This study documents differences in fish assemblages for 32 freshwater streams located between 258 and 2242 m a.s.l. on the eastern slopes of the central range of the Colombian Andes. A total of 2049 fishes belonging to 62 species, 34 genera and 16 families were collected. Species richness declined rapidly with altitude; nearly 90% of the species were recorded between 250 and 1250 m a.s.l. Three of the four physico-chemical variables, of the water, temperature, dissolved oxygen and pH, explained 53.5% of the variation in species richness along the altitudinal gradient, with temperature the most important (37.6%). An analysis of species composition showed that the distinctiveness of the fish fauna increased with elevation, with the greatest turnover observed between 1000 and 1750 m a.s.l. On this altitudinal gradient, turnover was dominated by the loss of species rather than gain, and dominance by just a few species was greater at higher elevations. Turnover was also observed along the altitudinal gradient in the structure of the three functional groups (torrential, pool and pelagic species). The study focused on understanding the pattern of diversity of fish communities inhabiting the Andes in Colombia. Anthropogenic effects on the altitudinal distribution of fish species in the region, however, are largely unknown and would require further investigations.

  13. Mitochondrial Variation among the Aymara and the Signatures of Population Expansion in the Central Andes

    PubMed Central

    BATAI, KEN; WILLIAMS, SLOAN R.

    2015-01-01

    Objectives The exploitation of marine resources and intensive agriculture led to a marked population increase early in central Andean prehistory. Constant historic and prehistoric population movements also characterize this region. These features undoubtedly affected regional genetic variation, but the exact nature of these effects remains uncertain. Methods Mitochondrial DNA (mtDNA) hypervariable region I sequence variation in 61 Aymara individuals from La Paz, Bolivia, was analyzed and compared to sequences from 47 other South American populations to test hypotheses of whether increased female effective population size and gene flow influenced the mtDNA variation among central Andean populations. Results The Aymara and Quechua were genetically diverse showing evidence of population expansion and large effective population size, and a demographic expansion model fits the mtDNA variation found among central Andean populations well. Estimated migration rates and the results of AMOVA and multidimensional scaling analysis suggest that female gene flow was also an important factor, influencing genetic variation among the central Andeans as well as lowland populations from western South America. mtDNA variation in south central Andes correlated better with geographic proximity than with language, and fit a population continuity model. Conclusion The mtDNA data suggests that the central Andeans experienced population expansion, most likely because of rapid demographic expansion after introduction of intensive agriculture, but roles of female gene flow need to be further explored. PMID:24449040

  14. Cold Episodes, Their Precursors and Teleconnections in the Central Peruvian Andes (1958-2009)

    NASA Astrophysics Data System (ADS)

    Sulca, J. C.; Vuille, M. F.; Trasmonte, G.; Silva, Y.; Takahashi, K.

    2014-12-01

    The Mantaro valley (MV) is located in the central Peruvian Andes. Occasionally, cold episodes are observed during the austral summer (January-March), which strongly damage crops. However, little is known about the causes and impacts of such cold episodes in the MV. The main goal of this study is thus to characterize cold episodes in the MV and assess their large-scale circulation and teleconnections over South America (SA) during austral summer. To identify cold events in the MV daily minimum temperature for the period 1958-2009 from Huayao station, located within the MV was used. We defined a cold episode as the period when daily minimum temperature drops below the 10-percentile for at least one day. Several gridded reanalysis and satellite products were used to characterize the large-scale circulation, cloud cover and rainfall over SA associated with these events for same period. Cold episodes in the MV are associated with positive OLR anomalies, which extend over much of the central Andes, indicating reduced convective cloud cover during these extremes, but also affirm the large-scale nature of these events. At the same time, northeastern Brazil (NEB) registers negative OLR anomalies, strong convective activity and enhanced cloud cover because displacement of the South Atlantic Convergence Zone (SACZ) toward the northeast of its climatologic position. Further, it is associated with a weakening of the Bolivian High - Nordeste Low (BH-NL) system at upper levels, but also influenced by a low-level migratory high-pressure center develops at 30°S, 50°W; propagating from mid- to low latitudes as part of an extratropical Rossby wave train. In conclusion, cold episodes in the MV appear to be caused by radiative cooling associated with reduced cloudiness, rather than cold air advection. The reduced cloud cover in turn results from a robust large-scale pattern of westerly wind anomalies over central Peruvian Andes, inhibiting moisture influx, convective activity and

  15. Evolution of Rhyolite at Laguna del Maule, a Rapidly Inflating Volcanic Field in the Southern Andes

    NASA Astrophysics Data System (ADS)

    Andersen, N. L.; Singer, B. S.; Jicha, B. R.; Hildreth, E. W.; Fierstein, J.; Rogers, N. W.

    2012-12-01

    The Laguna del Maule Volcanic Field (LdM) is host to both the foremost example of post-glacial rhyolitic volcanism in the southern Andes and rapid, ongoing crustal deformation. The flare-up of high-silica eruptions was coeval with deglaciation at 24 ka. Rhyolite and rhyodacite domes and coulees totaling 6.5 km3 form a 20 km ring around the central lake basin. This spatial and temporal concentration of rhyolite is unprecedented in the history of the volcanic field. Colinear major and trace element variation suggests these lavas share a common evolutionary history (Hildreth et al., 2010). Moreover, geodetic observations (InSAR & GPS) have identified rapid inflation centered in the western side of the rhyolite dome ring at a rate of 17 cm/year for five years, which has accelerated to 30 cm/yr since April 2012. The best fit to the geodetic data is an expanding magma body located at 5 km depth (Fournier et al., 2010; Le Mevel, 2012). The distribution of high-silica volcanism, most notably geochemically similar high-silica rhyolite lavas erupted 12 km apart of opposite sides of the lake within a few kyr of each other, raises the possibility that the shallow magma intrusion represents only a portion of a larger rhyolitic body, potentially of caldera forming dimensions. We aim to combine petrologic models with a precise geochronology to formulate a model of the evolution of the LdM magma system to its current state. New 40Ar/39Ar age determinations show rhyolitic volcanism beginning at 23 ka with the eruption of the Espejos rhyolite, followed by the Cari Launa Rhyolite at 14.5 ka, two flows of the Barrancas complex at 6.4 and 3.9 ka, and the Divisoria rhyolite at 2.2 ka. In contrast, significant andesitic and dacitic volcanism is largely absent from the central basin of LdM since the early post-glacial period suggesting a coincident basin-wide evolution from andesite to dacite to rhyolite and is consistent with a shallow body of low-density rhyolite blocking the eruption

  16. Novel Strain of Andes Virus Associated with Fatal Human Infection, Central Bolivia

    PubMed Central

    Cruz, Cristhopher D.; Vallejo, Efrain; Agudo, Roberto; Vargas, Jorge; Blazes, David L.; Guevara, Carolina; Laguna-Torres, V. Alberto; Halsey, Eric S.; Kochel, Tadeusz J.

    2012-01-01

    To better describe the genetic diversity of hantaviruses associated with human illness in South America, we screened blood samples from febrile patients in Chapare Province in central Bolivia during 2008–2009 for recent hantavirus infection. Hantavirus RNA was detected in 3 patients, including 1 who died. Partial RNA sequences of small and medium segments from the 3 patients were most closely related to Andes virus lineages but distinct (<90% nt identity) from reported strains. A survey for IgG against hantaviruses among residents of Chapare Province indicated that 12.2% of the population had past exposure to >1 hantaviruses; the highest prevalence was among agricultural workers. Because of the high level of human exposure to hantavirus strains and the severity of resulting disease, additional studies are warranted to determine the reservoirs, ecologic range, and public health effect of this novel strain of hantavirus. PMID:22515983

  17. Landsat Thematic Mapper observations of debris avalanche deposits in the Central Andes

    NASA Technical Reports Server (NTRS)

    Francis, P. W.; Wells, G. L.

    1988-01-01

    Remote sensing with the Landsat Thematic Mapper of debris avalanche deposits in the Central Andes between 18 and 27 deg S revealed, for the first time, the presence of 28 breached volcanic cones and 11 major volcanic debris avalanche deposits, several of which cover areas in excess of 100 sq km. It is concluded that such avalanche deposits are normal products of the evolution of large composite volcanoes, comparable with lava and pyroclastic flow deposits. A statistical survey of 578 composite volcanoes in the same area indicated that a majority of cones which achieve edifice heights between 2000 and 3000 m may undergo sector collapse. The paper describes morphological criteria for identifying breached composite cones and volcanic debris avalanches using orbital images.

  18. Subduction and collision processes in the Central Andes constrained by converted seismic phases.

    PubMed

    Yuan, X; Sobolev, S V; Kind, R; Oncken, O; Bock, G; Asch, G; Schurr, B; Graeber, F; Rudloff, A; Hanka, W; Wylegalla, K; Tibi, R; Haberland, C; Rietbrock, A; Giese, P; Wigger, P; Röwer, P; Zandt, G; Beck, S; Wallace, T; Pardo, M; Comte, D

    The Central Andes are the Earth's highest mountain belt formed by ocean-continent collision. Most of this uplift is thought to have occurred in the past 20 Myr, owing mainly to thickening of the continental crust, dominated by tectonic shortening. Here we use P-to-S (compressional-to-shear) converted teleseismic waves observed on several temporary networks in the Central Andes to image the deep structure associated with these tectonic processes. We find that the Moho (the Mohorovicić discontinuity--generally thought to separate crust from mantle) ranges from a depth of 75 km under the Altiplano plateau to 50 km beneath the 4-km-high Puna plateau. This relatively thin crust below such a high-elevation region indicates that thinning of the lithospheric mantle may have contributed to the uplift of the Puna plateau. We have also imaged the subducted crust of the Nazca oceanic plate down to 120 km depth, where it becomes invisible to converted teleseismic waves, probably owing to completion of the gabbro-eclogite transformation; this is direct evidence for the presence of kinetically delayed metamorphic reactions in subducting plates. Most of the intermediate-depth seismicity in the subducting plate stops at 120 km depth as well, suggesting a relation with this transformation. We see an intracrustal low-velocity zone, 10-20 km thick, below the entire Altiplano and Puna plateaux, which we interpret as a zone of continuing metamorphism and partial melting that decouples upper-crustal imbrication from lower-crustal thickening.

  19. Subduction and collision processes in the Central Andes constrained by converted seismic phases.

    PubMed

    Yuan, X; Sobolev, S V; Kind, R; Oncken, O; Bock, G; Asch, G; Schurr, B; Graeber, F; Rudloff, A; Hanka, W; Wylegalla, K; Tibi, R; Haberland, C; Rietbrock, A; Giese, P; Wigger, P; Röwer, P; Zandt, G; Beck, S; Wallace, T; Pardo, M; Comte, D

    The Central Andes are the Earth's highest mountain belt formed by ocean-continent collision. Most of this uplift is thought to have occurred in the past 20 Myr, owing mainly to thickening of the continental crust, dominated by tectonic shortening. Here we use P-to-S (compressional-to-shear) converted teleseismic waves observed on several temporary networks in the Central Andes to image the deep structure associated with these tectonic processes. We find that the Moho (the Mohorovicić discontinuity--generally thought to separate crust from mantle) ranges from a depth of 75 km under the Altiplano plateau to 50 km beneath the 4-km-high Puna plateau. This relatively thin crust below such a high-elevation region indicates that thinning of the lithospheric mantle may have contributed to the uplift of the Puna plateau. We have also imaged the subducted crust of the Nazca oceanic plate down to 120 km depth, where it becomes invisible to converted teleseismic waves, probably owing to completion of the gabbro-eclogite transformation; this is direct evidence for the presence of kinetically delayed metamorphic reactions in subducting plates. Most of the intermediate-depth seismicity in the subducting plate stops at 120 km depth as well, suggesting a relation with this transformation. We see an intracrustal low-velocity zone, 10-20 km thick, below the entire Altiplano and Puna plateaux, which we interpret as a zone of continuing metamorphism and partial melting that decouples upper-crustal imbrication from lower-crustal thickening. PMID:11140679

  20. Cosmogenic Nuclide Studies And Geomorphological Implications In The Hyperarid Central Western Andes, Northern Chile

    NASA Astrophysics Data System (ADS)

    Kober, F.; Schlunegger, F.; Ivy-Ochs, S.; Baur, H.; Wieler, R.; Kubik, P. W.; Schneider, H.

    2003-12-01

    We have conducted geomorphological and cosmogenic nuclide studies in the central Andes of Northern Chile (Arica area) in order to quantify landscape evolution at the Western Andean Escarpment. The area is characterized by broad abandoned middle to late Miocene plains that are cut by deeply incised rivers. The major phase of incision has been active since ca. 8 My with different magnitudes and accelerated backward erosion forces through time. Important processes must have been a base level change in the Coastal Cordillera area and climatic changes driven by orogenic growth. Fluvial incision rates are ca. 50m/My across the Escarpment during the middle/late Miocene and early Pliocene and about two to four times higher from the Pliocene until the present, especially in more distal parts relative to the pinned base level control (enhanced backward erosion). Bedrock erosion rates on the broad plains determined with cosmogenic nuclides are several orders of magnitude lower than fluvial incision rates. Erosion rates of ignimbrites determined by paired studies of radionuclides (10Be, 26Al) and stable 21Ne are 10 to 100cm/My at medium elevations and increase towards the high Andes to >250cm/My. This increase is largely controlled by the effect of orographic precipitation that correlates with increasing rates and intensities of rainfall towards the Western Cordillera. Coastal areas, subjected only to coastal fog, show abandoned hanging rivers and smoothed diffusive hillslopes. These landscapes exhibit also extremely low cosmogenically derived erosion rates (<100cm/My). Therefore, the large parts of the landscapes at the northern tip of the Atacama Desert have retained their relict landscape aspect since they formed in Middle Micocene. The comparison of river incision and bedrock erosion clearly shows a strong decoupling between both geomorphic landscape units. A change towards a coupled system can only be found in the high, rainy parts of the Andes (>3500m), which are

  1. Modeling Soil Organic Carbon Variation Along Climatic and Topographic Trajectories in the Central Andes

    NASA Astrophysics Data System (ADS)

    Gavilan, C.; Grunwald, S.; Quiroz, R.; Zhu, L.

    2015-12-01

    The Andes represent the largest and highest mountain range in the tropics. Geological and climatic differentiation favored landscape and soil diversity, resulting in ecosystems adapted to very different climatic patterns. Although several studies support the fact that the Andes are a vast sink of soil organic carbon (SOC) only few have quantified this variable in situ. Estimating the spatial distribution of SOC stocks in data-poor and/or poorly accessible areas, like the Andean region, is challenging due to the lack of recent soil data at high spatial resolution and the wide range of coexistent ecosystems. Thus, the sampling strategy is vital in order to ensure the whole range of environmental covariates (EC) controlling SOC dynamics is represented. This approach allows grasping the variability of the area, which leads to more efficient statistical estimates and improves the modeling process. The objectives of this study were to i) characterize and model the spatial distribution of SOC stocks in the Central Andean region using soil-landscape modeling techniques, and to ii) validate and evaluate the model for predicting SOC content in the area. For that purpose, three representative study areas were identified and a suite of variables including elevation, mean annual temperature, annual precipitation and Normalized Difference Vegetation Index (NDVI), among others, was selected as EC. A stratified random sampling (namely conditioned Latin Hypercube) was implemented and a total of 400 sampling locations were identified. At all sites, four composite topsoil samples (0-30 cm) were collected within a 2 m radius. SOC content was measured using dry combustion and SOC stocks were estimated using bulk density measurements. Regression Kriging was used to map the spatial variation of SOC stocks. The accuracy, fit and bias of SOC models was assessed using a rigorous validation assessment. This study produced the first comprehensive, geospatial SOC stock assessment in this

  2. Energy Balance of High Altitude Glaciarised Basins In The Central Andes: Climatic and Hydrological Aspects

    NASA Astrophysics Data System (ADS)

    Corripio, J.; Purves, R.

    The Central Andes of Chile and Argentina can be classified as climatic deserts, yet they support very large populations and a rich agriculture, thanks to melt water from snow melt and glaciers. Meteorological data from one automatic weather station in- stalled on two different glaciers at 3300m and 4600m a.s.l. in the Chilean Andes (700 W, 330 S), are presented and discussed. The relative importance of the terms in the en- ergy balance equation shows substantial differences from that of mid-latitude Alpine glaciers, with turbulent heat transfer accounting for 10 to 20% of the net energy bal- ance. Extremely low relative humidity (up to 8%) and moderate winds result in high evaporation rates. Intense evaporation, together with effective radiative cooling, dew point well below freezing and intense solar radiation favour differential ablation of the snow surface, which results in the formation of snow penitentes, these unique forms result in a further modification of the energy balance. The intense solar radia- tion enhances the effect of the surrounding topography on snow-covered areas, which is modelled using terrain algorithms for digital elevation models. Stable conditions and a clear atmosphere permit effective use of solar radiative models with good re- sults. Remoteness and lack of infrastructures complicate access, which was made us- ing traditional transportation methods in the region: mules! Lack of data and limited budget was partially overcome by developing an alternative simple and economical remote sensing tool for snow cover monitoring and albedo estimation using terrestrial photography. Finally, the output of a distributed snow melt model is compared to dis- charge data from a glacier whose outflow is monitored by the Chilean Water Board, as it is the main source of drinking water for Santiago de Chile.

  3. Trench investigation along the Merida section of the Bocono fault (central Venezuelan Andes), Venezuela

    USGS Publications Warehouse

    Audemard, F.; Pantosti, D.; Machette, M.; Costa, C.; Okumura, K.; Cowan, H.; Diederix, H.; Ferrer, C.

    1999-01-01

    The Bocono fault is a major NE-SW-trending, dextral fault that extends for about 500 km along the backbone of the Venezuelan Andes. Several large historical earthquakes in this region have been attributed to the Bocono fault, and some of these have been recently associated with specific parts through paleoseismologic investigations. A new trench study has been performed, 60 km to the northeast of Merida in the central Venezuelan Andes, where the fault forms a releasing bend, comprising two conspicuous late Holocene fault strands that are about 1 km apart. The southern and northern strands carry about 70% and 30% (respectively) of the 7-10 mm/yr net slip rate measured in this sector, which is based on a 40 vs. 85-100 m right-lateral offset of the Late Pleistocene Los Zerpa moraines. A trench excavated on the northern strand of the fault (near Morros de los Hoyos, slightly northeast of Apartaderos) across a twin shutter ridge and related sag pond exposed two main fault zones cutting Late Pleistocene alluvial and Holocene peat deposits. Each zone forms a shutter ridge with peat deposits ponded against the uplifted block. The paleoearthquake reconstruction derived from this trench allow us to propose the occurrence of at least 6-8 earthquakes in the past 9000 yr, yielding a maximum average recurrence interval of about 1100-1500 yr. Based on the northern strands average slip rate (2.6 mm/yr), such as earthquake sequence should have accommodated about 23 m of slip since 9 ka, suggesting that the maximum slip per event ranges between 3 and 4 m. No direct evidence for the large 1812 earthquake has been found in the trench, although this earthquake may have ruptured this section of the fault. Further paleoseismic studies will investigate the possibility that this event occurred in the Bocono fault, but ruptured mainly its southern strand in this region.

  4. Interseismic coupling and seismic potential along the Central Andes subduction zone

    NASA Astrophysics Data System (ADS)

    Chlieh, Mohamed; Perfettini, Hugo; Tavera, Hernando; Avouac, Jean-Philippe; Remy, Dominique; Nocquet, Jean-Mathieu; Rolandone, FréDéRique; Bondoux, Francis; Gabalda, Germinal; Bonvalot, Sylvain

    2011-12-01

    We use about two decades of geodetic measurements to characterize interseismic strain build up along the Central Andes subduction zone from Lima, Peru, to Antofagasta, Chile. These measurements are modeled assuming a 3-plate model (Nazca, Andean sliver and South America Craton) and spatially varying interseismic coupling (ISC) on the Nazca megathrust interface. We also determine slip models of the 1996 Mw = 7.7 Nazca, the 2001 Mw = 8.4 Arequipa, the 2007 Mw = 8.0 Pisco and the Mw = 7.7 Tocopilla earthquakes. We find that the data require a highly heterogeneous ISC pattern and that, overall, areas with large seismic slip coincide with areas which remain locked in the interseismic period (with high ISC). Offshore Lima where the ISC is high, a Mw˜8.6-8.8 earthquake occurred in 1746. This area ruptured again in a sequence of four Mw˜8.0 earthquakes in 1940, 1966, 1974 and 2007 but these events released only a small fraction of the elastic strain which has built up since 1746 so that enough elastic strain might be available there to generate a Mw > 8.5 earthquake. The region where the Nazca ridge subducts appears to be mostly creeping aseismically in the interseismic period (low ISC) and seems to act as a permanent barrier as no large earthquake ruptured through it in the last 500 years. In southern Peru, ISC is relatively high and the deficit of moment accumulated since the Mw˜8.8 earthquake of 1868 is equivalent to a magnitude Mw˜8.4 earthquake. Two asperities separated by a subtle aseismic creeping patch are revealed there. This aseismic patch may arrest some rupture as happened during the 2001 Arequipa earthquake, but the larger earthquakes of 1604 and 1868 were able to rupture through it. In northern Chile, ISC is very high and the rupture of the 2007 Tocopilla earthquake has released only 4% of the elastic strain that has accumulated since 1877. The deficit of moment which has accumulated there is equivalent to a magnitude Mw˜8.7 earthquake. This study thus

  5. Surface exposure dating of moraines and alluvial fans in the Southern Central Andes

    NASA Astrophysics Data System (ADS)

    Terrizzano, Carla; Zech, Roland; García Morabito, Ezequiel; Haghipour, Negar; Christl, Marcus; Likermann, Jeremías; Tobal, Jonathan; Yamin, Marcela

    2016-04-01

    The role of tectonics versus climate in controlling the evolution of alluvial fans in discussed controversially. The southern Central Andes and their forelands provide a perfect setting to study climate versus tectonic control of alluvial fans. On the one hand, the region is tectonically active and alluvial fan surfaces are offset by faults. The higher summits, on the other hand, are glaciated today, and glacial deposits document past periods of lower temperatures and increased precipitation. We applied 10Be surface exposure dating on 5 fan terraces 4 moraines of the Ansilta range (31.6°S - 69.8°W) using boulders and amalgamated pebbles to explore their chronological relationship. From youngest to oldest, the alluvial fan terraces yield minimum ages of 15 ± 1 ka (T1), 97 ± 9 ka (T2), 141 ± 9 ka (T3), 286 ± 14 ka (T4) and 570 ± 57 ka (T5). Minimum ages derived from moraines are 14 ± 1 ka (M1), 22 ± 2 ka (M2), 157 ± 14 ka (M3) and 351 ± 33 ka (M4), all calculations assuming no erosion and using the scaling scheme for spallation based on Lal 1991, Stone 2000. The moraines document glacial advances during cold periods at the marine isotope stages (MIS) 2, 6 and 10. The terraces T1, T3 seem to be geomorphologic counterparts during MIS 2 and 6. We suggest that T2, T4 and T5 document aggradation during the cold periods MIS 5d, 8 and 14 in response to glacial advances, although the respective moraines are not preserved. Our results highlight: i) the arid climate in the Southern Central Andes favors the preservation of glacial and alluvial deposits allowing landscape and climate reconstructions back to ~570 ka), ii) alluvial deposits correlate with moraines or fall into cold glacial times, so that climate, and in particular the existence of glaciers, seems to be the main forcing of alluvial fan formation at our study site. References Lal, D., 1991: Cosmic ray labeling of erosion surfaces: In situ nuclide production rates and erosion models. Earth and Planetary

  6. Surface uplift and convective rainfall along the southern Central Andes (Angastaco Basin, NW Argentina)

    NASA Astrophysics Data System (ADS)

    Pingel, Heiko; Mulch, Andreas; Alonso, Ricardo N.; Cottle, John; Hynek, Scott A.; Poletti, Jacob; Rohrmann, Alexander; Schmitt, Axel K.; Stockli, Daniel F.; Strecker, Manfred R.

    2016-04-01

    Stable-isotopic and sedimentary records from the orogenic Puna Plateau of NW Argentina and adjacent intermontane basins to the east furnish a unique late Cenozoic record of range uplift and ensuing paleoenvironmental change in the south-central Andes. Today, focused precipitation in this region occurs along the eastern, windward flanks of the Eastern Cordillera and Sierras Pampeanas ranges, while the orogen interior constitutes high-elevation regions with increasingly arid conditions in a westward direction. As in many mountain belts, such hydrologic and topographic gradients are commonly mirrored by a systematic relationship between the oxygen and hydrogen stable isotope ratios of meteoric water and elevation. The glass fraction of isotopically datable volcanic ash intercalated in sedimentary sequences constitutes an environmental proxy that retains a signal of the hydrogen-isotopic composition of ancient precipitation. This isotopic composition thus helps to elucidate the combined climatic and tectonic processes associated with topographic growth, which ultimately controls the spatial patterns of precipitation in mountain belts. However, between 25.5 and 27°S present-day river-based hydrogen-isotope lapse rates are very low, possibly due to deep-convective seasonal storms that dominate runoff. If not accounted for, the effects of such conditions on moisture availability in the past may lead to misinterpretations of proxy-records of rainfall. Here, we present hydrogen-isotope data of volcanic glass (δDg), extracted from 34 volcanic ash layers in different sedimentary basins of the Eastern Cordillera and the Sierras Pampeanas. Combined with previously published δDg records and our refined U-Pb and (U-Th)/He zircon geochronology on 17 tuff samples, we demonstrate hydrogen-isotope variations associated with paleoenvironmental change in the Angastaco Basin, which evolved from a contiguous foreland to a fault-bounded intermontane basin during the late Mio

  7. Evidence of Teleconnections between the Peruvian central Andes and Northeast Brazil during extreme rainfall events

    NASA Astrophysics Data System (ADS)

    Sulca, J. C.; Vuille, M. F.; Silva, F. Y.; Takahashi, K.

    2013-12-01

    Knowledge about changes in regional circulation and physical processes associated with extreme rainfall events in South America is limited. Here we investigate such events over the Mantaro basin (MB) located at (10°S-13°S; 73°W-76°W) in the central Peruvian Andes and Northeastern Brazil (NEB), located at (9°S-15°S; 39°W-46°W). Occasional dry and wet spells can be observed in both areas during the austral summer season. The main goal of this study is to investigate potential teleconnections between extreme rainfall events in MB and NEB during austral summer. We define wet (dry) spells as periods that last for at least 3 (5) consecutive days with rainfall above (below) the 70 (30) percentile. To identify the dates of ocurrence of these events, we used daily accumulated rainfall data from 14 climate stations located in the Mantaro basin for the period 1965 to 2002. In NEB we defined a rainfall index which is based on average daily gridded rainfall data within the region for the same period. Dry (wet spells) in the MB are associated with positive (negative) OLR anomalies which extend over much of the tropical Andes, indicating the large-scale nature of these events. At 200 hPa anomalous easterly (westerly) zonal winds aloft accompany wet (dry) spells. Composite anomalies of dry spells in MB reveal significant contemporaneous precipitation anomalies of the opposite sign over NEB, which suggest that intraseasonal precipitation variability over the two regions may be dynamically linked. Indeed upper-tropospheric circulation anomalies over the central Andes extend across South America and appear to be tied to an adjustment in the Bolivian High-Nordeste Low system. Dry (wet) spells in NEB are equally associated with a large-scale pattern of positive (negative) OLR anomalies; however, there are no related significant OLR anomalies over the MB during these events. Dry (wet) spells are associated with robust patterns of anomalous wind fields at both low and upper

  8. Geometric evolution of the Horcones Inferior Glacier (Mount Aconcagua, Central Andes) during the 2002-2006 surge

    NASA Astrophysics Data System (ADS)

    Pitte, Pierre; Berthier, Etienne; Masiokas, Mariano H.; Cabot, Vincent; Ruiz, Lucas; Ferri Hidalgo, Lidia; Gargantini, Hernán.; Zalazar, Laura

    2016-01-01

    The Central Andes of Chile and Argentina (31-35°S) contain a large number and variety of ice masses, but only two surging glaciers have been studied in this region. We analyzed the 2002-2006 surge of the Horcones Inferior Glacier, Mount Aconcagua, Argentina, based on medium spatial resolution (15-30 m) satellite images and digital elevation models. During the buildup phase the glacier was stagnant, with velocities lower than 0.1 m/d. In the active-phase velocities reached 14 m/d and the glacier front advanced 3.1 km. At the peak of the active phase (2003-2004), the area-averaged elevation change was -42 m in the reservoir zone (2.53 km2) and +30 m in the receiving zone (3.31 km2). The estimated ice flux through a cross section located at 4175 meter above sea level was 108 m3 during a period of 391 days, a flux that suggests a mean glacier thickness at this location of ~90 m. The depletion phase showed a recovery of the reservoir zone elevation, the down wasting of the receiving zone (-17 m, 2007-2014), and a return to quiescent velocities. The short active phase, the abrupt change in the velocities, and the high level of the proglacial stream indicate a hydrological switch (Alaska type) trigger. The 2002-2006 and 1984-1990 surges of Horcones Inferior were synchronous with the surges of nearby Grande del Nevado Glacier. These events occurred after periods of positive mass balance, so we hypothesize a climate driver.

  9. The Basement of the Central Andes: The Arequipa and Related Terranes

    NASA Astrophysics Data System (ADS)

    Ramos, Victor A.

    2008-05-01

    The basement of the Central Andes provides insights for the dispersal of Rodinia, the reconstruction of Gondwana, and the dynamics of terrane accretion along the Pacific. The Paleoproterozoic Arequipa terrane was trapped during collision between Laurentia and Amazonia in the Mesoproterozoic. Ultrahigh-temperature metamorphism correlates with the collapse of the Sunsás-Grenville orogen after 1000 Ma and is related to slab break-off and dispersal of Rodinia. The Antofalla terrane separated in the Neoproterozoic, forming the Puncoviscana basin. Its closure was coeval with the collision of the eastern Sierras Pampeanas. The rift-drift transitions of the early Paleozoic clastic platform showed a gradual younging to the north, in agreement with counterclockwise rotation based on paleomagnetic data of Antofalla. North of Arequipa arc magmatism and high-grade metamorphism are linked to collision of the Paracas terrane in the Ordovician, during the Famatinian orogeny in the Sierras Pampeanas. The early Paleozoic history of the Arequipa massif is explained by a backarc, which further south changed to open oceanic conditions and subsequent collision. The Antofalla terrane reaccreted to the continental margin by the late Ordovician. These accretions and subsequent separations during the Mesoproterozoic, Neoproterozoic early Cambrian, and late Cambrian middle Ordovician are explained by changes in absolute motion of the Gondwana supercontinent during plate global reorganization.

  10. Snow Cover Quantification in the Central Andes Derived from Multi-Sensor Data

    NASA Astrophysics Data System (ADS)

    Cortés, G.; Cornwell, E.; McPhee, J. P.; Margulis, S. A.

    2014-12-01

    In this work we analyze time series of MODIS MOD10A1 and Landsat fractional snow cover images over the central-southern Andes (30°-34°S) with the objective of quantifying snow cover persistence over the region. Data from 2000-2011 is analyzed, and a snow cover persistence index (SCPI) is computed for each pixel at different resolutions over four test watersheds. The annual SCPI is calculated as the number of acquisitions during a year on which a pixel is covered by a fraction of snow greater than a defined threshold. We calculate the SCPI at the nominal Landsat resolution (30m) and at the MODIS resolution (500m) for each of the pixels of the different watersheds and for different thresholds. Furthermore, for each watershed, the correlation of SCPI with slope, aspect and elevation is calculated for Landsat at 30m, and aggregated at 100m and 500m, and for MODIS at 500m. Both MODIS and Landsat show significant differences in annual SCPI for the 500m resolution. The difference in correlation between SCP and physiographic variables is largest when comparing Landsat 30m to MODIS, suggesting that sensor resolution is an important limiting factor for the analyzed region. Trend analysis using both products show differences in terms of changes in SCPI for the 2000-2011 period, however the conclusions are not robust due to the short period analyzed.

  11. A new species of Phrynopus (Anura: Craugastoridae) from the central Peruvian Andes.

    PubMed

    Mamani, Luis; Malqui, Sergio

    2014-01-01

    We describe a new species of Phrynopus from the humid grassland of Distrito de Comas, Provincia Concepcion, Department of Junin. The new species is diagnosed by the lack of dentigerous processes of vomers, tympanic annulus and membrane imperceptible through the skin, males with nuptial pads and vocal slits, warty dorsal skin, and aerolate throat, belly and ventral surfaces of thighs, by possessing pronounced subconical tubercles in the post-tympanic area, by having rounded finger and toe tips with no disc structure, and by its overall dark brown to black coloration with few white and yellow spots in the dorsum and a dark-brown belly with white to gray blotches. Specimens were found under stones at a single area of the central Peruvian Andes at elevations between 4205-4490 m.a.s.l. The eggs had an average diameter of 4.3 mm. With the description and naming of the new species, the genus Phrynopus now contains 26 species, all of them endemic to Peru, and five of which are restricted to Departamento Junin. PMID:25081770

  12. Hydrothermal System of the Lastarria Volcano (Central Andes) Imaged by Magnetotellurics

    NASA Astrophysics Data System (ADS)

    Diaz, D.

    2015-12-01

    Lazufre volcanic complex, located in the central Andes, is recently undergoing an episode of uplift, conforming one of the most extensive deforming volcanic systems worldwide. Recent works have focused on the subsurface of this volcanic system at different scales, using surface deformation data, seismic noise tomography and magnetotellurics. Here we image the electrical resistivity structure of the Lastarria volcano, one of the most important features in the Lazufre area, using broadband magnetotelluric data at 30 locations around the volcanic edifice. Results from 3-D modeling show a conductive zone at 6 km depth south of the Lastarria volcano interpreted as a magmatic heat source, which is connected to a shallower conductive area beneath the volcanic edifice and its close vicinity. This shallow highly conductive zone fits with geochemical analysis results of thermal fluid discharges, related to fumaroles present in this area, in terms of depth extent and possible temperatures of fluids, and presents also a good correlation with seismic tomography results. The horizontal extension of this shallow conductive zone, related to the hydrothermal system of Lastarria, suggests that it has been draining one of the lagoons in the area (Laguna Azufrera), forming a sulfur rich area which can be observed at the southern side of this lagoon. Joint modeling of the hydrothermal system using magnetotellurics and seismic data is part of the current work.

  13. A satellite geodetic survey of large-scale deformation of volcanic centres in the central Andes.

    PubMed

    Pritchard, Matthew E; Simons, Mark

    2002-07-11

    Surface deformation in volcanic areas usually indicates movement of magma or hydrothermal fluids at depth. Stratovolcanoes tend to exhibit a complex relationship between deformation and eruptive behaviour. The characteristically long time spans between such eruptions requires a long time series of observations to determine whether deformation without an eruption is common at a given edifice. Such studies, however, are logistically difficult to carry out in most volcanic arcs, as these tend to be remote regions with large numbers of volcanoes (hundreds to even thousands). Here we present a satellite-based interferometric synthetic aperture radar (InSAR) survey of the remote central Andes volcanic arc, a region formed by subduction of the Nazca oceanic plate beneath continental South America. Spanning the years 1992 to 2000, our survey reveals the background level of activity of about 900 volcanoes, 50 of which have been classified as potentially active. We find four centres of broad (tens of kilometres wide), roughly axisymmetric surface deformation. None of these centres are at volcanoes currently classified as potentially active, although two lie within about 10 km of volcanoes with known activity. Source depths inferred from the patterns of deformation lie between 5 and 17 km. In contrast to the four new sources found, we do not observe any deformation associated with recent eruptions of Lascar, Chile. PMID:12110886

  14. Accommodation of shortening in southern central Andes: a multiscale structural approach

    NASA Astrophysics Data System (ADS)

    Branellec, Matthieu; Jean-Paul, Callot; Bertrand, Nivière; Charles, Aubourg; Jean-Claude, Ringenbach

    2016-04-01

    The Malargue fold and thrust belt is located in the northern part of the Neuquén basin in the Central Andes of Argentina. A full structural analysis of this hybrid thin and thick-skinned fold belt has been undertaken using several methods that cover a wide range of spatial and temporal scales. The way in which shortening was accommodated in the upper crust has first been investigated on a regional basis by means of cross sections building. Several field examples show that localization of deformation on rift-related inherited structure is frequent allowing us to target a common mode of deformation propagation. The structural geometries and the associated mechanisms governing during the Miocene shortening phase were subsequently compared to the present day pattern of active deformation enabling us to state about whether or not deformational mechanisms are continuous through times. In addition, meter-scale and millimetre-scale deformation were analysed thank to fracturing and Anisotropy of Magnetic Susceptibility data. Respectively, both of these methods shed new light on (1) the record of the several LPS related convergence phases that affected the Andean retro-arc since the late Cretaceous and (2) the relationships between the matrix strain pattern and the large scale distribution of macroscopic deformation.

  15. Geodetic observations of megathrust earthquakes and backarc wedge deformation across the central Andes

    NASA Astrophysics Data System (ADS)

    Weiss, J. R.; Brooks, B. A.; Foster, J. H.; Bevis, M. G.; Echalar, A.; Caccamise, D.; Heck, J. M.

    2014-12-01

    High-precision Global Positioning System (GPS) data offer an opportunity to investigate active orogenic wedges yet surface velocity fields are available for only a few examples worldwide. More observations are needed to link deformation processes across multiple timescales and to better understand strain accumulation and release in active wedge settings. Here we present a new GPS velocity field for the central Andes and the backarc orogenic wedge comprising the southern Subandes of Bolivia (SSA), a region previously thought to be mostly isolated from the plate boundary earthquake cycle. The time span of our observations (2000 to mid-2014) includes two megathrust earthquakes along the Chile trench that affected the SSA. The 2007 Mw 7.7 Tocopilla, Chile earthquake resulted in a regional postseismic decrease in the eastward component of horizontal surface velocities. Preliminary analysis of the deformation field from the April 01 2014 Mw 8.2 Pisagua, Chile earthquake also indicates a postseismic signal extending into the SSA. We create an interseismic velocity field for the SSA by correcting campaign GPS site velocities for the seasonal cycles estimated from continuous GPS site time series. We remove the effects of both megathrust events by estimating coseismic steps and fitting linear and logarithmic functions to the postseismic GPS site motions. The velocity estimates at most locations increase after correcting for the transients. This finding suggests that forces leading to shortening and earthquakes in the backarc wedge are not as temporally consistent as previously considered.

  16. Future runoff from glacierized catchments in the Central Andes could substantially decrease

    NASA Astrophysics Data System (ADS)

    Kronenberg, Marlene; Schauwecker, Simone; Huggel, Christian; Salzmann, Nadine; Drenkhan, Fabian; Frey, Holger; Giráldez, Claudia; Gurgiser, Wolfgang; Kaser, Georg; Suarez, Wilson; García Hernández, Javier; Fluixá-Sanmartín, Javier; Ayros, Edwin; Rohrer, Mario

    2016-04-01

    In Peru, about 50% of the energy is produced from hydropower plants. An important amount of this energy is produced with water from glaciated catchments. In these catchments river streamflow is furthermore needed for other socio-economic activities such as agriculture. However, the amount and seasonality of water from glacial melt is expected to undergo strong changes. As glaciers are projected to further decline with continued warming, runoff will become more and more sensitive to possible changes in precipitation patterns. Moreover, as stated by a recent study (Neukom et al., 2015), wet season precipitation sums in the Central Andes could decrease up to 19-33 % by the end of the 21st century compared to present-day conditions. Here, we investigate future runoff availability for selected glacierized catchments in the Peruvian Andes. In a first step, we apply a simplified energy balance and runoff model (ITGG-2.0-R) for current conditions. Thereafter, we model future runoff for different climate scenarios, including the possibility of strongly reduced precipitation. Preliminary findings indicate (i) changes in the seasonal distribution of runoff and (ii) significant reductions of the annual runoff in future for the mentioned scenario with significant precipitation decreases. During early phases of glacier recession, melt leads to increased runoff - respectively compensates for the precipitation reduction in the corresponding scenario - depending on the fraction of catchment glaciation. Glaciers are acting as natural water reservoirs and may buffer the decreasing precipitation in glacierized catchments for a limited period. However, strongly reduced precipitation will have noticeable consequences on runoff, particularly when glacier melt contribution gets smaller and finally is completely missing. This will have consequences on the water availability for hydropower production, agriculture, mining and other water uses. Critical conditions may emerge in particular

  17. Classification of debris-covered glaciers and rock glaciers in the Andes of central Chile

    NASA Astrophysics Data System (ADS)

    Janke, Jason R.; Bellisario, Antonio C.; Ferrando, Francisco A.

    2015-07-01

    In the Dry Andes of Chile (17 to 35° S), debris-covered glaciers and rock glaciers are differentiated from true glaciers based on the percentage of surface debris cover, thickness of surface debris, and ice content. Internal ice is preserved by an insulating cover of thick debris, which acts as a storage reservoir to release water during the summer and early fall. These landforms are more numerous than glaciers in the central Andes; however, the existing legislation only recognizes uncovered or semicovered glaciers as a water resource. Glaciers, debris-covered glaciers, and rock glaciers are being altered or removed by mining operations to extract valuable minerals from the mountains. In addition, agricultural expansion and population growth in this region have placed additional demands on water resources. In a warmer climate, as glaciers recede and seasonal water availability becomes condensed over the course of a snowmelt season, rock glaciers and debris-covered glaciers contribute a larger component of base flow to rivers and streams. As a result, identifying and locating these features to implement sustainable regional planning for water resources is important. The objective of this study is to develop a classification system to identify debris-covered glaciers and rock glaciers based on the interpretation of satellite imagery and aerial photographs. The classification system is linked to field observations and measurements of ice content. Debris-covered glaciers have three subclasses: surface coverage of semi (class 1) and fully covered (class 2) glaciers differentiates the first two forms, whereas debris thickness is critical for class 3 when glaciers become buried with more than 3 m of surface debris. Based on field observations, the amount of ice decreases from more than 85%, to 65-85%, to 45-65% for semi, fully, and buried debris-covered glaciers, respectively. Rock glaciers are characterized by three stages. Class 4 rock glaciers have pronounced

  18. Genome of Plant Maca (Lepidium meyenii) Illuminates Genomic Basis for High-Altitude Adaptation in the Central Andes.

    PubMed

    Zhang, Jing; Tian, Yang; Yan, Liang; Zhang, Guanghui; Wang, Xiao; Zeng, Yan; Zhang, Jiajin; Ma, Xiao; Tan, Yuntao; Long, Ni; Wang, Yangzi; Ma, Yujin; He, Yuqi; Xue, Yu; Hao, Shumei; Yang, Shengchao; Wang, Wen; Zhang, Liangsheng; Dong, Yang; Chen, Wei; Sheng, Jun

    2016-07-01

    Maca (Lepidium meyenii Walp, 2n = 8x = 64), belonging to the Brassicaceae family, is an economic plant cultivated in the central Andes sierra in Peru (4000-4500 m). Considering that the rapid uplift of the central Andes occurred 5-10 million years ago (Ma), an evolutionary question arises regarding how plants such as maca acquire high-altitude adaptation within a short geological period. Here, we report the high-quality genome assembly of maca, in which two closely spaced maca-specific whole-genome duplications (WGDs; ∼6.7 Ma) were identified. Comparative genomic analysis between maca and closely related Brassicaceae species revealed expansions of maca genes and gene families involved in abiotic stress response, hormone signaling pathway, and secondary metabolite biosynthesis via WGDs. The retention and subsequent functional divergence of many duplicated genes may account for the morphological and physiological changes (i.e., small leaf shape and self-fertility) in maca in a high-altitude environment. In addition, some duplicated maca genes were identified with functions in morphological adaptation (i.e., LEAF CURLING RESPONSIVENESS) and abiotic stress response (i.e., GLYCINE-RICH RNA-BINDING PROTEINS and DNA-DAMAGE-REPAIR/TOLERATION 2) under positive selection. Collectively, the maca genome provides useful information to understand the important roles of WGDs in the high-altitude adaptation of plants in the Andes. PMID:27174404

  19. The paradigm of paraglacial megafans of the San Juan river basin, Central Andes, Argentina

    NASA Astrophysics Data System (ADS)

    Suvires, Graciela M.

    2014-11-01

    The spatial distribution and several morphometric characteristics of the Quaternary alluvial fans of the San Juan River, in the province of San Juan, at the Central and Western part of Argentina, have been studied to classify them as paraglacial megafans, as well to ratify its depositional environmental conditions. The high sedimentary load exported by San Juan river from the Central Andes to the foreland depressions is estimated about 3,682,200 hm3. The large alluvial fans of Ullum-Zonda and Tulum valleys were deposited into deep tectonic depressions, during the Upper Pleistocene deglaciation stages. The outcome of collecting remotely sensed data, map and DEM data, geophysical data and much fieldwork gave access to morphometric, morphographic and morphogenetic data of these alluvial fans. The main drainage network was mapped on processed images using QGis (vers.2.0.1). Several fan morphometric parameters were measured, such as the size, the shape, the thickness, the surface areas and the sedimentary volume of exported load. The analyzed fans were accumulated in deep tectonic depressions, where the alluvium fill reaches 700 to 1200 m thick. Such fans do not reach the large size that other world megafans have, and this is due to tectonic obstacles, although the sedimentary fill average volume surpasses 514,000 hm3. The author proposes to consider Ullum-Zonda and Tulum alluvial fans as paraglacial megafans. According to the stratigraphic relationships of the tropical South American Rivers, the author considers that the San Juan paraglacial megafans would have occurred in the period before 24 ka BP , possibly corresponding to Middle Pleniglacial (ca 65-24ka BP). They record colder and more humid conditions compared with the present arid and dry conditions.

  20. Preliminary Results From the CAUGHT Experiment: Investigation of the North Central Andes Subsurface Using Receiver Functions and Ambient Noise Tomography

    NASA Astrophysics Data System (ADS)

    Ryan, J. C.; Ward, K. M.; Porter, R. C.; Beck, S. L.; Zandt, G.; Wagner, L. S.; Minaya, E.; Tavera, H.

    2011-12-01

    Jamie Ryan, Kevin M. Ward, Ryan Porter, Susan Beck, George Zandt, Lara Wagner, Estela Minaya, and Hernando Tavera The University of Arizona The University of North Carolina San Calixto Observatorio, La Paz, Bolivia IGP, Lima, Peru In order to investigate the interplay between crustal shortening, lithospheric removal, and surface uplift we have deployed 50 broadband seismometers in northwestern Bolivia and southern Peru as part of the interdisciplinary Central Andean Uplift and Geodynamics of High Topography (CAUGHT) project. The morphotectonic units of the central Andes from west to east, consist of the Western Cordillera, the active volcanic arc, the Altiplano, an internally drained basin (~4 km elevation), the Eastern Cordillera, the high peaks (~6 km elevation) of an older fold and thrust belt, the Subandean zone, the lower elevation active fold and thrust belt, and the foreland Beni basin. Between northwestern Bolivia and southern Peru, the Altiplano pinches out north of Lake Titicaca as the Andes narrow northward. The CAUGHT seismic instruments were deployed between 13° to 18° S latitudes to investigate the crust and mantle lithosphere of the central Andes in this transitional zone. In northwest Bolivia, perpendicular to the strike of the Andes, there is a total of 275 km of documented upper crustal shortening (15° to 17°S) (McQuarrie et al, 2008). Associated with the shortening is crustal thickening and possibly lithospheric removal as the thickening lithospheric root becomes unstable. An important first order study is to compare upper crustal shortening estimates with present day crustal thickness. To estimate crustal thickness, we have calculated receiver functions using an iterative deconvolution method and used common conversion point stacking along the same profile as the geologically based shortening estimates. In our preliminary results, we observed a strong P to S conversion corresponding to the Moho at approximately 60-65 km depth underneath the

  1. Tectonomagmatic characteristics of the back-arc portion of the Calama-Olacapato-El Toro Fault Zone, Central Andes

    NASA Astrophysics Data System (ADS)

    Acocella, V.; Gioncada, A.; Omarini, R.; Riller, U.; Mazzuoli, R.; Vezzoli, L.

    2011-06-01

    Post-20 Ma magmatism in the Central Andes is either localized in the magmatic arc or distributed east of it, on the Altiplano-Puna Plateau. Here there is a distinct concentration of magmatic centers on NW-SE trending lineaments, such as the Calama-Olacapato-El Toro (COT), that extends into the Eastern Cordillera to the east of the Puna. Understanding the possible genetic relationship between prominent structures and magmatic centers on these lineaments is important to elucidate the tectonomagmatic evolution of the Central Andes. We investigated the back-arc area of the COT using remote sensing, geological, structural, and petrochemical data. Our study demonstrates that this portion of the COT consists of NW-SE striking faults, formed under overall left-lateral transtension that decreases in activity toward the COT termini. Deformation on the COT occurred during and after activity of prominent N-S striking transpressive fault systems and is coeval with magmatism, which is focused on the central COT. The most evolved magmatic rocks, with an upper crustal imprint, are exposed on the central COT, whereas more primitive, mantle-derived mafic to moderately evolved magmatic rocks, are found toward the COT termini. This points to a genetic relationship between upper crustal deformation and magmatic activity that led to enhanced magma storage in the central COT. COT magmas may result either from slab steepening or episodic delamination of the asthenospheric mantle.

  2. Comparative phylogeography of co-distributed Phrygilus species (Aves, Thraupidae) from the Central Andes.

    PubMed

    Álvarez-Varas, R; González-Acuña, D; Vianna, J A

    2015-09-01

    The Neotropical ecoregion has been an important place of avian diversification where dispersal and allopatric events coupled with periods of active orogeny and climate change (Late Pliocene-Pleistocene) have shaped the biogeography of the region. In the Neotropics, avian population structure has been sculpted not only by geographical barriers, but also by non-allopatric factors such as natural selection and local adaptation. We analyzed the genetic variation of six co-distributed Phrygilus species from the Central Andes, based on mitochondrial and nuclear markers in conjunction with morphological differentiation. We examined if Phrygilus species share patterns of population structure and historical demography, and reviewed the intraspecific taxonomy in part of their geographic range. Our results showed different phylogeographic patterns between species, even among those belonging to the same phylogenetic clade. P. alaudinus, P. atriceps, and P. unicolor showed genetic differentiation mediated by allopatric mechanisms in response to specific geographic barriers; P. gayi showed sympatric lineages in northern Chile, while P. plebejus and P. fruticeti showed a single genetic group. We found no relationship between geographic range size and genetic structure. Additionally, a signature of expansion was found in three species related to the expansion of paleolakes in the Altiplano region and the drying phase of the Atacama Desert. Morphological analysis showed congruence with molecular data and intraspecific taxonomy in most species. While we detected genetic and phenotypic patterns that could be related to natural selection and local adaptation, our results indicate that allopatric events acted as a major factor in the population differentiation of Phrygilus species.

  3. Multi-sensor geophysical constraints on crustal melt in the central Andes: the PLUTONS project

    NASA Astrophysics Data System (ADS)

    Pritchard, M. E.; Comeau, M. J.; West, M. E.; Christensen, D. H.; Mcfarlin, H. L.; Farrell, A. K.; Del Potro, R.; Gottsmann, J.; McNutt, S. R.; Michelfelder, G.; Diez, M.; Elliott, J.; Henderson, S. T.; Keyson, L.; Delgado, F.; Unsworth, M. J.

    2015-12-01

    The central Andes is a key global location to quantify storage, transport, and volumes of magma in the Earth's crust as it is home to the world's largest zone of partial melt (the Altiplano-Puna Magma or Mush Body, APMB) as well as the more recently documented Southern Puna Magma Body (SPMB). We describe results from the recently completed international PLUTONS project that focused inter-disciplinary study on two sites of large-scale surface uplift that presumably represent ongoing magmatic intrusions in the mid to upper crust - Uturuncu, Bolivia (in the center of the APMB) and Lazufre on the Chile-Argentina border (on the edge of the SPMB). In particular, a suite of geophysical techniques (seismology, gravity, surface deformation, and electro-magnetic methods) have been used to infer the current subsurface distribution and quantity of partial melts in combination with geochemical and lab studies on samples from the area. Both Uturuncu and Lazufre show separate geophysical anomalies in the upper and mid/lower crust (e.g., low seismic velocity, low resistivity, etc.) indicating multiple distinct reservoirs of magma and/or hydrothermal fluids with different properties. The characteristics of the geophysical anomalies differ somewhat depending on the technique used - reflecting the different sensitivity of each method to subsurface melt of different compositions, connectivity, and volatile content. For example, the depth to the top of the APMB is shallower in a joint ambient noise tomography and receiver function analysis compared to a 3D magnetotelluric inversion. One possibility is that the seismic methods are detecting brines above the APMB that do not have a large electromagnetic signature. Comparison of the geophysical measurements with laboratory experiments at the APMB indicate a minimum of 4-25% melt averaged over the region is needed -- higher melt volumes are permitted by the gravity and MT data and may exist in small regions. However, bulk melt values above

  4. Three-Dimensional Seismic Image of a Geothermal Prospect: Tinguiririca, Central Andes, Chile

    NASA Astrophysics Data System (ADS)

    Lira, E.; Comte, D.; Giavelli, A.; Clavero, J. E.; Pineda, G.

    2010-12-01

    Seismic monitoring has been widely used by the oil and gas industry, as a valuable input for the reservoir characterization. This tool has also been used in geothermal productive systems, particularly to understand permeability controls usually associated to shallow crustal fault systems that are seismically actives. Faults can be considered either “migration path” or “seals” in Petroleum Systems, depending on their activity story (they are carriers while actives and seals when the activity cease due to diagenetic processes in the fault plain). On the other hand, is well known that seismic velocities are strongly related to rock properties, in particular Vp/Vs and VpVs relationship has been successfully used to emphasize the variations in the physical rock properties due to fluid content and porosity. In geothermal systems, P and S-wave velocities are expected to be noticeably affected by massive hydrothermal alteration and/or to the presence of hot water in the fault related fractures of the rocks. In this job, the results of three months of seismic monitoring and a seismic velocity tomography are presented. Sixteen short period continuous recording, three components seismic stations were deployed in an area of approximately 20x10 Km2, and a large 8.8 magnitude earthquake took place during the recording period. The study area corresponds to the Tinguiririca volcanic complex (70°21''W, 35°48''S), in the high mountain of the Central Andes near the Chile-Argentina border. These preliminary results are complemented with some MT profiles, delineating potentially interesting geothermal features.

  5. Comparative phylogeography of co-distributed Phrygilus species (Aves, Thraupidae) from the Central Andes.

    PubMed

    Álvarez-Varas, R; González-Acuña, D; Vianna, J A

    2015-09-01

    The Neotropical ecoregion has been an important place of avian diversification where dispersal and allopatric events coupled with periods of active orogeny and climate change (Late Pliocene-Pleistocene) have shaped the biogeography of the region. In the Neotropics, avian population structure has been sculpted not only by geographical barriers, but also by non-allopatric factors such as natural selection and local adaptation. We analyzed the genetic variation of six co-distributed Phrygilus species from the Central Andes, based on mitochondrial and nuclear markers in conjunction with morphological differentiation. We examined if Phrygilus species share patterns of population structure and historical demography, and reviewed the intraspecific taxonomy in part of their geographic range. Our results showed different phylogeographic patterns between species, even among those belonging to the same phylogenetic clade. P. alaudinus, P. atriceps, and P. unicolor showed genetic differentiation mediated by allopatric mechanisms in response to specific geographic barriers; P. gayi showed sympatric lineages in northern Chile, while P. plebejus and P. fruticeti showed a single genetic group. We found no relationship between geographic range size and genetic structure. Additionally, a signature of expansion was found in three species related to the expansion of paleolakes in the Altiplano region and the drying phase of the Atacama Desert. Morphological analysis showed congruence with molecular data and intraspecific taxonomy in most species. While we detected genetic and phenotypic patterns that could be related to natural selection and local adaptation, our results indicate that allopatric events acted as a major factor in the population differentiation of Phrygilus species. PMID:25987531

  6. Ocean-Atmosphere Coupled Model Simulations of Precipitation in the Central Andes

    NASA Technical Reports Server (NTRS)

    Nicholls, Stephen D.; Mohr, Karen I.

    2015-01-01

    The meridional extent and complex orography of the South American continent contributes to a wide diversity of climate regimes ranging from hyper-arid deserts to tropical rainforests to sub-polar highland regions. In addition, South American meteorology and climate are also made further complicated by ENSO, a powerful coupled ocean-atmosphere phenomenon. Modelling studies in this region have typically resorted to either atmospheric mesoscale or atmosphere-ocean coupled global climate models. The latter offers full physics and high spatial resolution, but it is computationally inefficient typically lack an interactive ocean, whereas the former offers high computational efficiency and ocean-atmosphere coupling, but it lacks adequate spatial and temporal resolution to adequate resolve the complex orography and explicitly simulate precipitation. Explicit simulation of precipitation is vital in the Central Andes where rainfall rates are light (0.5-5 mm hr-1), there is strong seasonality, and most precipitation is associated with weak mesoscale-organized convection. Recent increases in both computational power and model development have led to the advent of coupled ocean-atmosphere mesoscale models for both weather and climate study applications. These modelling systems, while computationally expensive, include two-way ocean-atmosphere coupling, high resolution, and explicit simulation of precipitation. In this study, we use the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST), a fully-coupled mesoscale atmosphere-ocean modeling system. Previous work has shown COAWST to reasonably simulate the entire 2003-2004 wet season (Dec-Feb) as validated against both satellite and model analysis data when ECMWF interim analysis data were used for boundary conditions on a 27-9-km grid configuration (Outer grid extent: 60.4S to 17.7N and 118.6W to 17.4W).

  7. Giant magmatic water reservoir beneath Uturuncu volcano and Altiplano-Puna region (Central Andes)

    NASA Astrophysics Data System (ADS)

    Laumonier, Mickael; Gaillard, Fabrice; Muir, Duncan; Blundy, Jon; Unsworth, Martyn

    2016-04-01

    Volcanism at continental arcs is the surface manifestation of long-lived crustal magmatic processes whereby mantle-derived hydrous basalt magma differentiates to more silica-rich magmas by a combination of crystallization and crustal melting. What erupts is just a fraction of the total volume of magma produced by these processes; the unerupted, plutonic residues solidify and are inaccessible to direct study until millions of years of uplift and erosion bring them to the surface. In contrast, geophysical surveys, using electromagnetic and seismic waves, can provide real-time images of subduction zone magmatic systems. Several such studies have revealed that arc volcanoes are underlain by large partially molten regions at depths of >10 km, the largest known example being the Altiplano-Puna magma body (APMB) in central Andes. Interpreting such geophysical images in terms of amount, composition and distribution of partial melts is limited by our lack of knowledge of the physical properties of silicate melts at elevated pressures and temperatures. Here we present high-pressure, in situ experimental data showing that the electrical conductivity of andesitic melts is primarily controlled by their dissolved water contents. Linking our new measurements to petrological constraints from andesites erupted on the Altiplano, we show that the APMB is composed of 10-20% of an andesitic melt containing 8-10 wt% dissolved water. This implies that the APMB is a giant water anomaly in the global subduction system, with a total mass of dissolved magmatic water about half of the water contained within the Adriatic Sea. In addition to the controls on the physical properties of the melts, the abundance of dissolved water governs the structural levels of magma ponding, equivalent to the depth of water saturation, where degassing and crystallisation promote partial melting and weakening of the upper crust. Unexpectedly, very high concentrations of water in andesite magmas shall impede their

  8. Neogene paleoelevation of intermontane basins in a narrow, compressional mountain range, southern Central Andes of Argentina

    NASA Astrophysics Data System (ADS)

    Hoke, Gregory D.; Giambiagi, Laura B.; Garzione, Carmala N.; Mahoney, J. Brian; Strecker, Manfred R.

    2014-11-01

    The topographic growth of mountain ranges at convergent margins results from the complex interaction between the motion of lithospheric plates, crustal shortening, rock uplift and exhumation. Constraints on the timing and magnitude of elevation change gleaned from isotopic archives preserved in sedimentary sequences provide insight into how these processes interact over different timescales to create topography and potentially decipher the impact of topography on atmospheric circulation and superposed exhumation. This study uses stable isotope data from pedogenic carbonates collected from seven different stratigraphic sections spanning different tectonic and topographic positions in the range today, to examine the middle to late Miocene history of elevation change in the central Andes thrust belt, which is located immediately to the south of the Altiplano-Puna Plateau, the world's second largest orogenic plateau. Paleoelevations are calculated using previously published local isotope-elevation gradients observed in modern rainfall and carbonate-formation temperatures determined from clumped isotope studies in modern soils. Calculated Neogene basin paleoelevations are between 1 km and 1.9 km for basins that today are located between 1500 and 3400 m elevation. Considering the modern elevation and δ18O values of precipitation at the sampling sites, three of the intermontane basins experienced surface uplift between the end of deposition during the late Miocene and present. The timing of elevation change cannot be linked to any documented episodes of large-magnitude crustal shortening. Paradoxically, the maximum inferred surface uplift in the core of the range is greatest where the crust is thinnest. The spatial pattern of surface uplift is best explained by eastward migration of a crustal root via ductile deformation in the lower crust and is not related to flat-slab subduction.

  9. A paleolimnological perspective on industrial-era metal pollution in the central Andes, Peru.

    PubMed

    Cooke, Colin A; Abbott, Mark B

    2008-04-15

    To date, few studies have investigated the environmental legacy associated with industrialization in the South American Andes. Here, we present an environmental archive of industrial pollution from (210)Pb-dated lake cores recovered from Laguna Chipian, located near the Cerro de Pasco metallurgical region and Laguna Pirhuacocha, located near the Morococha mining region and the La Oroya smelting complex. At Laguna Chipian, trace metal concentrations increase beginning ~1900 AD, coincident with the construction of the central Peruvian railway, and the rapid industrial development of the Cerro de Pasco region. Trace metal concentrations and fluxes peak during the 1950s before subsequently declining up-core (though remaining well above background levels). While Colonial mining and smelting operations are known to have occurred at Cerro de Pasco since at least 1630 AD, our sediment record preserves no associated metal deposition. Based on our (14)C and (210)Pb data, we suggest that this is due to a depositional hiatus, rather than a lack of regional Colonial pollution. At Laguna Pirhuacocha, industrial trace metal deposition first begins ~1925 AD, rapidly increasing after ~1950 AD and peaking during either the 1970s or 1990s. Trace metal concentrations from these lakes are comparable to some of the most polluted lakes in North America and Europe. There appears to be little diagenetic alteration of the trace metal record at either lake, the exception being arsenic (As) accumulation at Laguna Pirhuacocha. There, a correlation between As and the redox-sensitive element manganese (Mn) suggests that the sedimentary As burden is undergoing diagenetic migration towards the sediment-water interface. This mobility has contributed to surface sediment As concentrations in excess of 1100 microg g(-1). The results presented here chronicle a rapidly changing Andean environment, and highlight a need for future research in the rate and magnitude of atmospheric metal pollution. PMID

  10. Drought increases the freezing resistance of high-elevation plants of the Central Chilean Andes.

    PubMed

    Sierra-Almeida, Angela; Reyes-Bahamonde, Claudia; Cavieres, Lohengrin A

    2016-08-01

    Freezing temperatures and summer droughts shape plant life in Mediterranean high-elevation habitats. Thus, the impacts of climate change on plant survival for these species could be quite different to those from mesic mountains. We exposed 12 alpine species to experimental irrigation and warming in the Central Chilean Andes to assess whether irrigation decreases freezing resistance, irrigation influences freezing resistance when plants are exposed to warming, and to assess the relative importance of irrigation and temperature in controlling plant freezing resistance. Freezing resistance was determined as the freezing temperature that produced 50 % photoinactivation [lethal temperature (LT50)] and the freezing point (FP). In seven out of 12 high-Andean species, LT50 of drought-exposed plants was on average 3.5 K lower than that of irrigated plants. In contrast, most species did not show differences in FP. Warming changed the effect of irrigation on LT50. Depending on species, warming was found to have (1) no effect, (2) to increase, or (3) to decrease the irrigation effect on LT50. However, the effect size of irrigation on LT50 was greater than that of warming for almost all species. The effect of irrigation on FP was slightly changed by warming and was sometimes in disagreement with LT50 responses. Our data show that drought increases the freezing resistance of high-Andean plant species as a general plant response. Although freezing resistance increases depended on species-specific traits, our results show that warmer and moister growing seasons due to climate change will seriously threaten plant survival and persistence of these and other alpine species in dry mountains.

  11. Drought increases the freezing resistance of high-elevation plants of the Central Chilean Andes.

    PubMed

    Sierra-Almeida, Angela; Reyes-Bahamonde, Claudia; Cavieres, Lohengrin A

    2016-08-01

    Freezing temperatures and summer droughts shape plant life in Mediterranean high-elevation habitats. Thus, the impacts of climate change on plant survival for these species could be quite different to those from mesic mountains. We exposed 12 alpine species to experimental irrigation and warming in the Central Chilean Andes to assess whether irrigation decreases freezing resistance, irrigation influences freezing resistance when plants are exposed to warming, and to assess the relative importance of irrigation and temperature in controlling plant freezing resistance. Freezing resistance was determined as the freezing temperature that produced 50 % photoinactivation [lethal temperature (LT50)] and the freezing point (FP). In seven out of 12 high-Andean species, LT50 of drought-exposed plants was on average 3.5 K lower than that of irrigated plants. In contrast, most species did not show differences in FP. Warming changed the effect of irrigation on LT50. Depending on species, warming was found to have (1) no effect, (2) to increase, or (3) to decrease the irrigation effect on LT50. However, the effect size of irrigation on LT50 was greater than that of warming for almost all species. The effect of irrigation on FP was slightly changed by warming and was sometimes in disagreement with LT50 responses. Our data show that drought increases the freezing resistance of high-Andean plant species as a general plant response. Although freezing resistance increases depended on species-specific traits, our results show that warmer and moister growing seasons due to climate change will seriously threaten plant survival and persistence of these and other alpine species in dry mountains. PMID:27053321

  12. Assessment of Paleozoic terrane accretion along the southern central Andes using detrital zircon geochronology

    NASA Astrophysics Data System (ADS)

    McKenzie, R.; Horton, B. K.; Fuentes, F.; Fosdick, J. C.; Capaldi, T.; Stockli, D. F.; Alvarado, P. M.

    2015-12-01

    Two distinct Paleozoic terranes known as Cuyania and Chilenia occupy the southern central Andes of Argentina and Chile. Because the proposed terrane boundaries coincide with major structural elements of the modern Andean system at 30-36°S, it is important to understand their origins and potential role in guiding later Andean deformation. The Cuyania terrane of western Argentina encompasses the Precordillera (PC) and a thick-skinned thrust block of the western Sierras Pampeanas, persisting southward to the San Rafael Basin (SRB). Although recently challenged, Cuyania has been long considered a piece of southern Laurentia that rifted away during the early Cambrian and collided with the Argentine margin during the Ordovician. Chilenia is situated west of Cuyania and includes the Frontal Cordillera (FC) and Andean magmatic arc. This less-studied terrane was potentially accreted during an enigmatic Devonian orogenic event. We present new detrital zircon U-Pb age data from siliciclastic sedimentary rocks that span the entire Paleozoic to Triassic from the FC, PC, and SRB. Cambrian rocks of the PC exhibit similar zircon age distributions with prominent ~1.4 and subordinate ~1.1 Ga populations, which are distinct from other Paleozoic strata. Plutonic rocks with these ages are common in southern Laurentia, whereas ~1.4 Ga zircons are uncommon in South American age distributions. This supports a Laurentian origin for Cuyania in isolation from Argentina during the Cambrian. Upper Paleozoic strata from the PC, FC, and SRB all yield similar age data suggesting shared provenance across the proposed Cuyania-Chilenia suture. Age distributions also notably lack Devonian-age grains. The regional paucity of Devonian plutonic rocks and detrital zircon casts doubt on a possible arc system between these terranes at this time, a key requisite for the mid-Paleozoic transfer and accretion of Chilenia to the Argentine margin. Collectively, these data question the precise boundaries of the

  13. A paleolimnological perspective on industrial-era metal pollution in the central Andes, Peru.

    PubMed

    Cooke, Colin A; Abbott, Mark B

    2008-04-15

    To date, few studies have investigated the environmental legacy associated with industrialization in the South American Andes. Here, we present an environmental archive of industrial pollution from (210)Pb-dated lake cores recovered from Laguna Chipian, located near the Cerro de Pasco metallurgical region and Laguna Pirhuacocha, located near the Morococha mining region and the La Oroya smelting complex. At Laguna Chipian, trace metal concentrations increase beginning ~1900 AD, coincident with the construction of the central Peruvian railway, and the rapid industrial development of the Cerro de Pasco region. Trace metal concentrations and fluxes peak during the 1950s before subsequently declining up-core (though remaining well above background levels). While Colonial mining and smelting operations are known to have occurred at Cerro de Pasco since at least 1630 AD, our sediment record preserves no associated metal deposition. Based on our (14)C and (210)Pb data, we suggest that this is due to a depositional hiatus, rather than a lack of regional Colonial pollution. At Laguna Pirhuacocha, industrial trace metal deposition first begins ~1925 AD, rapidly increasing after ~1950 AD and peaking during either the 1970s or 1990s. Trace metal concentrations from these lakes are comparable to some of the most polluted lakes in North America and Europe. There appears to be little diagenetic alteration of the trace metal record at either lake, the exception being arsenic (As) accumulation at Laguna Pirhuacocha. There, a correlation between As and the redox-sensitive element manganese (Mn) suggests that the sedimentary As burden is undergoing diagenetic migration towards the sediment-water interface. This mobility has contributed to surface sediment As concentrations in excess of 1100 microg g(-1). The results presented here chronicle a rapidly changing Andean environment, and highlight a need for future research in the rate and magnitude of atmospheric metal pollution.

  14. Wide-Angle Seismic Experiment Across the Oeste Fault Zone, Central Andes, Northern Chile.

    NASA Astrophysics Data System (ADS)

    Lorenzo, J. M.; Yáñez, G. A.; Vera, E. E.; Sepúlveda, J.

    2008-12-01

    From December 6-21, 2007, we conducted a 3-component, radio-telemetric, seismic survey along a ~ 15-km wide E-W transect in the Central Andes, at a latitude of ~ 22.41° S, centered north of the city of Calama (68.9° W), Chile. The study area is sandwiched between the Central Depression in the west and the Andean Western Cordillera of Chile. Recording stations, nominally spaced at intervals of either 125 or 250 m collected up to 3.5 s of refracted seismic arrivals at maximum source-receiver offsets exceeding 15 km. Ten shothole sources, spaced 2-6 km apart focused energy on the shallow (0-3 km), crustal, Paleogene-age structures. Preliminary, tomographic inversions of refracted first arrivals show the top of a shallow (< 1km), high- velocity (VP, ~5 km/s) crust, deepening sharply eastward to at least 2 km. At the surface, this central basement step correlates to a regionally extensive (> 600 km), strike-slip fault zone known as the Oeste fault. Turning ray densities suggest the base of the overlying velocity gradient unit (VP, 2-4 km/s) dips inwardly from both east and west directions toward the Oeste fault to depths of almost 1 km. Plate reorganization commencing at least by the latter half of the Oligocene led from oblique to more orthogonal convergence between the South American and the Nazca (Farallon) Plates. We interpret previously mapped, older, minor faults as being generated within the right-lateral, orogen-parallel, Oeste strike-slip fault zone, and postdated by Neogene, N-S striking thrust faults. In this context we also interpret that the spatial distribution of velocity units requires an period of extensional activity that may (1) postdate the transpressional strike slip fault activity of the Neogene, (2) be related to a later releasing bend through the translation and interaction of rigid blocks hidden at depth or even (3) be the consequence of inelastic failure from the result of flexural loading.

  15. Variation of the upper mantle velocity structure along the central-south Andes

    NASA Astrophysics Data System (ADS)

    Liang, Xiaofeng; Sandvol, Eric; Shen, Yang; Gao, Haiying

    2014-05-01

    Variations in the subduction angle of the Nazca plate beneath the South American plate has lead to different modes of deformation and volcanism along the Andean active margin. The volcanic gap between the central and southern Andean volcanic zones is correlated with the Pampean flat-slab subduction zone, where the subducting Nazca slab changes from a 30-degree dipping slab beneath the Puna plateau to a horizontal slab beneath the Sierras Pampeanas, and then to a 30-degree dipping slab beneath the south Andes from north to south. The Pampean flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of crustal deformation. A major Pliocene delamination event beneath the southern Puna plateau has previously been inferred from geochemical and geological and preliminary geophysical data. The mechanisms for the transition between dipping- and flat-subduction slab and the mountain building process of the central Andean plateau are key issues to understanding the Andean-type orogenic process. We use a new frequency-time normalization approach with non-linear stacking to extract very-broadband (up to 300 second) empirical Green's functions (EGFs) from continuous seismic records. The long-period EGFs provide the deeper depth-sensitivity needed to constrain the mantle structure. The broadband waveform data are from 393 portable stations of four temporary networks: PUNA, SIEMBRA, CHARGE, RAMP, East Sierras Pampeanas, BANJO/SEDA, REFUCA, ANCORP, and 31 permanent stations accessed from both the IRIS DMC and GFZ GEOFON DMC. A finite difference waveform propagation method is used to generate synthetic seismograms from 3-D velocity model. We use 3-D traveltime sensitivity kernels, and traveltime residuals measurement by waveform cross-correlation to directly invert the upper mantle shear-wave velocity structure. The preliminary model shows strong along-strike velocity variations within in the mantle wedge and

  16. Variation of the upper mantle velocity structure along the central-south Andes

    NASA Astrophysics Data System (ADS)

    Liang, X.; Sandvol, E. A.; Shen, Y.; Gao, H.; Zhang, Z.

    2013-12-01

    Variations in the subduction angle of the Nazca plate beneath the South American plate has lead to different modes of deformation and volcanism along the Andean active margin. The volcanic gap between the central and southern Andean volcanic zones is correlated with the Pampean flat-slab subduction zone, where the subducting Nazca slab changes from a 30-degree dipping slab beneath the Puna plateau to a horizontal slab beneath the Sierras Pampeanas, and then to a 30-degree dipping slab beneath the south Andes from north to south. The Pampean flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of crustal deformation. A major Pliocene delamination event beneath the southern Puna plateau has previously been inferred from geochemical, geological, and preliminary geophysical data. The mechanisms for the transition between dipping- and flat-subduction slab and the mountain building process of the central Andean plateau are key issues to understanding the Andean-type orogenic process. We use a new frequency-time normalization approach to extract very-broadband (up to 300 second) empirical Green's functions (EGFs) from continuous seismic records. The long-period EGFs provide the sensitivity needed to constrain the deep mantle structure. The broadband waveform data are from 393 portable stations of eight temporary networks: PUNA, SIEMBRA, CHARGE, RAMP, East Sierras Pampeanas, BANJO/SEDA, REFUCA, ANCORP, and 31 permanent stations accessed from both the IRIS DMC and GFZ GEOFON DMC. A finite difference wave propagation method is used to generate synthetic seismograms from 3-D velocity model. We use 3-D traveltime sensitivity kernels, and traveltime residuals measured by waveform cross-correlation to directly invert the upper mantle shear-wave velocity structure. The preliminary model shows strong along-strike velocity variations within in the mantle wedge and the subducting NAZCA slab. Low upper

  17. Central Andes mountains, Chile/Argentina as seen from STS-67

    NASA Technical Reports Server (NTRS)

    1995-01-01

    The Chilean coastline and the arid Atacama Desert stretch the length of the view with the high Andes on the eastern margin where hundreds of volcanoes dot the landscape. The wider (250-350 kilometers) Altiplano ('plains') sector of the Andes appears in the top half of the view, and the narrow (120 kilometers) 'mountain-chain-dominated' sector to the bottom. The northern half of Chile can be seen, with the 'hammer-head' peninsula at the city of Antofagasta, top left. Up welling of cold water as the Humboldt Current immediately offshore gives rise to low stratus cloud. The extensive cloud mass on the right lies beyond the Andes in the low country of Argentina's 'pampas' grasslands and Chaco semi-desert.

  18. Exceptional Isotopic Variability in Stream Waters of the Central Andes: Large-Scale or Local Controls?

    NASA Astrophysics Data System (ADS)

    Fiorella, R. P.; Poulsen, C. J.; Ehlers, T. A.; Jeffery, M. L.; Pillco Zola, R. S.

    2012-12-01

    Modern precipitation on the Altiplano in central South America shows large seasonal and interannual variability and is dominated by seasonal convection during austral summer. The stable isotopic compositions of oxygen and hydrogen in precipitation and surface waters may be useful in diagnosing atmospheric processes over the Altiplano as they reflect the atmospheric history of the water vapor forming precipitation. Few data exist about the spatial and temporal isotopic variability of precipitation or surface water in the region, however, and therefore, the controls governing isotope distribution over the Altiplano are poorly understood. Samples of stream water were collected from small catchments on the Altiplano and along two elevation transects on the eastern cordillera of the Andes (at 17°30' and 21°15'S) between April 2009 and April 2012. As precipitation over the Altiplano is highly seasonal and the environment is otherwise arid, the isotopic signature of these streams is thought integrate the composition of rainy season precipitation. We limit our analysis to ephemeral streams with no groundwater component. Sampled waters show high spatial and interannual isotopic variability. As expected, stream water becomes increasingly depleted with increased elevation along a transect, but the isotopic lapse rates along the two transects are different and show high interannual variability. The average isotopic lapse rate for the northern transect was 1.09‰/km, but varied from 0.79‰/km in 2010 to 1.36‰/km in 2011 (only collected 2010-2012), while the average isotopic lapse rate for the southern transect was 1.74‰/km and varied between 1.50‰/km in 2010 and 1.92‰/km in 2009. Across the Altiplano itself, stream water varies by over 10‰ (δ18O) within a single season (2011), and by over 13‰ across the entire collection period. The high spatial variability of the stream water isotopic composition on the Altiplano suggests that simple Rayleigh fractionation is

  19. A geophysical survey of active volcanism in the Central and Southern Andes

    NASA Astrophysics Data System (ADS)

    Jay, Jennifer Ann

    The subduction of the Nazca plate beneath the South American plate results in great earthquakes and active volcanism along the Andean margin. The Central Volcanic Zone (CVZ) between 15°S and 28°S and the Southern Volcanic Zone (SVZ) between 33°S and 46°S are separated by a zone of flat slab subduction and differ significantly in the manifestation of current volcanic activity. The CVZ has been considered less hazardous due to the few number of historical volcanic eruptions compared to the SVZ, yet it contains the largest mid-crustal magma body on Earth and erupted at least 10,000 km 3 of ignimbrite in the Late Miocene (10-1 Ma). In this dissertation, I use InSAR (interferometric synthetic aperture radar), thermal remote sensing, and seismology to investigate active volcanism in the Central and Southern Andes. InSAR and thermal remote sensing provide synoptic coverage along the volcanic arc, and seismic experiments allow further examination of selected volcanoes. I establish the first catalog of seismicity at Uturuncu volcano in Bolivia, where InSAR has observed continuous uplift since 1992, and find an unusually high seismicity rate for a Pleistocene volcano as well as swarm activity and triggered earthquakes. I then conduct a survey using satellite thermal infrared data to detect thermal hotspots related to volcanic activity throughout the CVZ and SVZ. I find hotspots at many volcanoes that had not previously been documented, with the CVZ containing more volcanoes with hotspots than the SVZ. One of the most thermally active volcanoes in the SVZ, Cordon Caulle volcano, experienced a large rhyodacitic eruption from 2011-2012. I use InSAR and petrology to model the pre-eruptive conditions at depth and co-eruptive processes and find that a large, long-lived crustal magma reservoir must be present beneath Cordon Caulle. Finally, I carry out an InSAR survey of volcanoes in southern Peru, completing a regional study of volcano deformation in the CVZ and allowing for a

  20. Reconstruction of cryospheric changes in the Maipo and Juncal river basins, central Andes of Chile: an integrative geomorphological approach

    NASA Astrophysics Data System (ADS)

    Nussbaumer, Samuel U.; García, Juan L.; Gómez, Gabriel; Vega, Rodrigo M.; Gärtner-Roer, Isabelle; Salzmann, Nadine

    2016-04-01

    Water in the central Andes (32-38° S), a semi-arid mountainous area with elevations over 6000 m asl., is of great importance and a critical resource especially in the dry summer months. Ice bodies, such as glaciers and rock glaciers (permafrost) in the high mountains, provide a substantial part of the fresh-water resources but also for intensive economical use for the lowlands including Santiago metropolitan region, Chile. However the evolution of these ice bodies since the last deglaciation (i.e., Holocene, last ˜12,000 years), and in particular during historical times, and their feedback with climate is fairly unknown. In view of projected climate change, this is striking because it is also unknown whether these natural resources could be used as sustainable fresh-water source in the future. Within the presented project, we develop and apply an integrative geomorphologic approach to study glaciers and their long-term evolution in the central Andes of Chile. Apart from glaciers (with variable debris-coverage), rock glaciers have evolved over time as striking geomorphological landforms in this area. We combine geomorphologic mapping using remote-sensing and in-situ data with an innovative surface exposure dating technique to determine the ages of distinct moraine ridges at three study sites in watersheds of the Santiago region: Juncal Norte, Loma Larga and Nieves Negras glaciers. First results of the project are presented, including a detailed geomorphological mapping and first analysis of the landform dynamics. At all three sites, we distinguished at least three moraine systems of a Holocene putative age. These prominent moraine belts show that glaciers were at least 5 km longer than at present. Deglaciation from these ice marginal positions was gradual and complex in response to the detrital cover on the glaciers. Differences in ice thickness of the main glaciers in the respective valleys amount to about 100 m. Due to the partial, extensive debris coverage, the

  1. Asynchronous Glacial Chronologies in the Central Andes (15-40°S) and Paleoclimatic Implications

    NASA Astrophysics Data System (ADS)

    Zech, R.; Kull, C.; Kubik, P. W.; Veit, H.

    2006-12-01

    We have established glacial chronologies along a N-S transect over the Central Andes using 10Be surface exposure dating. Our results show that maximum glacial advances occurred asynchronously and reflect the varying influence and shifts of the major atmospheric circulation systems during the Late Quaternary: the tropical circulation in the north and the westerlies in the south. In Bolivia (three research areas in the Cordillera Real and the Cordillera Cochabamba, ~15°S) glacial advances could be dated to ~20 and 12 ka BP. This is in good agreement with published exposure age data from moraines in Bolivia and Peru (provided that all ages are calculated following the same scaling system). Accordingly, the maximum glaciation there probably occurred roughly synchronous to the temperature minimum of the global Last Glacial Maximum (LGM) and the lateglacial cold reversals. Strict correlation with neither the Younger Dryas in the northern hemisphere, nor the Antarctic Cold Reversal is possible due to the current systematic exposure age uncertainties (~10%). Glacier-Climate-Modelling corroborates the sensitivity of the reconstructed glaciers to temperature changes, rather than precipitation. On the contrary, there is good evidence for the dominant role of precipitation changes on the glacial chronologies in the lee of the Cordillera Occidental, i.e. on the Altiplano and further south. The pronounced lateglacial wet phase, which is well documented in lake transgression phases as far south as 28°S (-> tropical moisture source), seems to have caused glacial advances even at ~30°S. In two research areas in Chile at that latitude, we were able to date several lateglacial moraines. Besides, the maximum datable glaciation there occurred at ~30 ka BP. That is significantly earlier than the LGM (sensu strictu) and points to favourable climate conditions for glaciation at that time (particularly increased precipitation). We conclude that the westerlies were more intensive or

  2. Regional distance shear-coupled PL propagation within the northern Altiplano, central Andes

    NASA Astrophysics Data System (ADS)

    Swenson, Jennifer L.; Beck, Susan L.; Zandt, George

    1999-12-01

    Properties of the shear-coupled P wavetrain (SPL) from regional earthquakes provide important information about the structure of the crust and upper mantle. We investigate broad-band seismic data from intermediate-depth earthquakes and develop a grid search technique using synthetic seismograms to study the sensitivity of SPL and to model the crustal structure of the northern Altiplano, central Andes. Waveforms from an earthquake that occurred on 1994 December 12 within the Nazca slab beneath the Altiplano display a clear SPL wavetrain at the temporary stations deployed during the BANJO and SEDA experiments. We relocate this event and determine the moment tensor by inverting the complete long-period waveforms. With these source parameters fixed, we perform sensitivity analyses using a reflectivity technique to compute synthetic seismograms at a distance of 313 km (BANJO station 2, SALI). We find that, at this distance, the long-period SPL wavetrain is sensitive to the following model parameters, in order of decreasing sensitivity: crustal VP/VS, mantle VP/VS, average crustal velocity, crustal thickness, focal depth, distance (location), crustal Qα and Qβ, and mantle velocity. We develop a grid search method to investigate the four parameters of the crust/upper mantle model to which the synthetic seismograms are most sensitive at SALI (crustal VP/VS, mantle VP/VS, average crustal velocity, crustal thickness). Trade-offs exist among all four of the model parameters, resulting in a range of acceptable crustal models that provide excellent fits between the data and synthetic seismograms in the passband of 15-100 s at a single station. However, by using data at a range of distances (150-450 km) we find that the model that provides the best overall fit between the data and synthetic seismograms, and thus best approximates the average characteristics of the crust and upper mantle structure of the northern Altiplano, is characterized by an average crustal velocity of 6

  3. Broadband regional waveform modeling to investigate crustal structure and tectonics of the central Andes

    NASA Astrophysics Data System (ADS)

    Swenson, Jennifer Lyn

    We use broadband regional waveform modeling of earthquakes in the central Andes to determine seismic properties of the Altiplano crust. Properties of the shear-coupled P-wavetrain (SPL ) from intermediate-depth events provide particularly important information about the structure of the crust. We utilize broadband seismic data recorded at the BANJO and SEDA stations, and synthetic seismograms computed with a reflectivity technique to study the sensitivity of SPL to crustal and upper mantle parameters at regional distances. We find that the long-period SPL-wavetrain is most sensitive to crustal and mantle Poisson's ratios, average crustal velocity, and crustal thickness. A comprehensive grid search method developed to investigate these four parameters suggests that although trade-offs exist between model parameters, models of the Altiplano which provide the best fit between the data and synthetic seismograms are characterized by low Poisson's ratios, low average crustal velocity and thick crust. We apply our grid search technique and sensitivity analysis results to model the full waveforms from 6 intermediate-depth and 2 shallow-focus earthquakes recorded at regional distances by BANJO and SEDA stations. Results suggest that the Altiplano crust is much thicker (55--65 km) and slower (5.75--6.25 km/s) than global average values. Low crustal and mantle Poisson's ratios together with the lack of evidence for a high-velocity lower crust suggests a bulk felsic crustal composition, resulting in an overall weak crust. Our results favor a model of crustal thickening involving large-scale tectonic shortening of a predominantly felsic crust. To better understand the mechanics of earthquake rupture along the South American subduction zone, we have analyzed broadband teleseismic P-waves and utilize single- and multi-station inversion techniques to constrain source characteristics for the 12 November 1996 Peru subduction zone earthquake. Aftershock locations, intensity reports

  4. Early Tertiary Exhumation, Erosion, and Sedimentation in the Central Andes, NW Argentina

    NASA Astrophysics Data System (ADS)

    Carrapa, B.; Decelles, P. G.; Gerhels, G.; Mortimer, E.; Strecker, M. R.

    2006-12-01

    Timing of deformation and resulting sedimentation patterns in the Altiplano-Puna Plateau-Eastern Cordillera of the southern Central Andes are the subject of ongoing controversial debate. In the Bolivian Altiplano, sedimentation into a foreland basin system commenced during the Paleocene. Farther south in the Puna and Eastern Cordillera of NW Argentina, a lack of data has precluded a similar interpretation. Early Tertiary non-marine sedimentary rocks are preserved within the present day Puna Plateau and Eastern Cordillera of NW Argentina. The Salar de Pastos Grandes basin in the Puna Plateau contains more than 2 km of Eocene alluvial and fluvial strata in the Geste Formation, deposited in close proximity to orogenic source terrains. Sandstone and conglomerate petrographic data document Ordovician quartzites and minor phyllites and schists as the main source rocks. Detrital zircon U-Pb ages from both the Geste Formation and from underlying Ordovician quartzite cluster in the 900-1200 Ma (Grenville) and late Precambrian-Cambrian (Panafrican) ranges. Sparse late Eocene (~37-34 Ma) grains are also present; their large size, euhedral shape, and decreasing mean ages upsection suggest that these grains are volcanogenic (i.e. ash fall contamination), derived from an inferred magmatic arc to the west. The Eocene ages corroborate mammalian paleontological dates, defining the approximate begin of deposition of the Geste Formation. Alternatively, these young zircons could be of plutonic origin; however, no Eocene plutons are present in the surrounding source rocks and this interpretation is not likely. From W to E, fluvial rocks of the Quebrada de los Colorados Formation show similar sedimentological features as those observed for the Geste Formation, suggesting a genetic link between the two. Detrital zircon U-Pb data show mainly Panafrican ages, with sparse ages in the 860-935 Ma range and a few mid-Proterozoic ages. More importantly, a significant number of late Eocene

  5. Structural control of the emplacement of the Portrerillos porphyry copper, central Andes of Chile

    NASA Astrophysics Data System (ADS)

    Niemeyer, Hans; Munizaga, Rodrigo

    2008-11-01

    The Potrerillos porphyry is located in the Late Eocene-Oligocene metallogenic belt of porphyry copper deposits of Chile, Cordillera de Domeyko, central Andes. It is formed of a porphyritic biotite-hornblende monzonite that was emplaced at less than 1000 m depth. The intrusion has a cylindrical vertical form at depth, whereas its uppermost section resembles a mushroom whose stem is inclined 20-25° to the northwest. The location of the Potrerillos porphyry coincides with a major facies and east-west thickness change in Jurassic to Late Cretaceous marine sedimentary and Tertiary volcanic host rocks. Structurally, the porphyry was emplaced at the intersection between the northeast-oriented Potrerillos fold-and-thrust belt, and a system of northwest-trending strike-slip faults of the Ciénaga fault system. Both structural elements are related to a sinistral regional transpression that was active during the Middle to Late Eocene. The north-northeast trending Sierra Castillo-Agua Amarga fault system was trench-linked with an oblique subduction along the Peru-Chile trench in the southwestern part of South America at this time. One of the main structural elements of the Potrerillos fold-and-thrust belt is the eastward verging Potrerillos Mine reverse fault. We demonstrate a syntectonic relationship between the Potrerillos porphyry emplacement and the onset of the Potrerillos Mine fault. The control at the shallowest levels of the Potrerillos porphyry emplacement was studied by means of a structural analysis of folds, cleavage and deformed oolites in the country rock. This analysis suggests that the porphyry occupied the core of an anticline. The form of this anticline was modeled as a fault-propagation-fold taking into account a 200 m displacement along the basal fault and a local shortening of 45.5% occurred. This model is compatible with a limited displacement along the Potrerillos Mine fault under hot, ductile conditions. The remaining displacement of 1600 m would have

  6. Modelling distributed ablation on Juncal Norte Glacier, dry Andes of central Chile

    NASA Astrophysics Data System (ADS)

    Carenzo, Marco; Pellicciotti, Francesca; Helbing, Jakob; Dadic, Ruzica; Burlando, Paolo

    2010-05-01

    In the Aconcagua River Basin, in the dry Andes of central Chile, water resources in summer originate mostly from snow and ice glacier melt. Summer seasons are dry and stable, with precipitation close to zero, low relative humidity and very intense solar radiation. The region's economic activities are dependent on these water resources, but their assessment is still incomplete and an effort is needed to evaluate present and future changes in water from glacier and seasonal snow covers in this area. The main aim of this paper is to simulate glacier melt and runoff from Juncal Norte Glacier, in the upper Aconcagua Basin, using models of various complexity and data requirement. We simulate distributed glacier ablation for two seasons using an energy-balance model (EB) and an enhanced temperature-index model (ETI). Meteorological variables measured at Automatic Weather Stations (AWSs) located on and off-glacier are extrapolated from point observations to the glacier-wide scale. Shortwave radiation is modelled with a parametric model taking into account shading, reflection from slopes and atmospheric transmittance. In the energy-balance model, the longwave radiation flux is computed from Stefan-Boltzmann relationships and turbulent fluxes are calculated using the bulk aerodynamic method. The EB model includes subsurface heat conduction and gravitational redistribution of snow. Glacier runoff is modelled using a linear reservoir approach accounting for the temporal evolution of the system. Hourly simulations of glacier melt are validated against ablation observations (ultrasonic depth gauge and ablation stakes) and runoff measured at the glacier snout is compared to a runoff record obtained from a combination of radar water level measurements and tracer experiments. Results show that extrapolation of meteorological input data, and of temperature in particular, is the largest source of model uncertainty, together with snow water equivalent initial conditions. We explore

  7. Eocene extensional exhumation of basement and arc rocks along southwesternmost Peru, Central Andes.

    NASA Astrophysics Data System (ADS)

    Noury, Mélanie; Bernet, Matthias; Sempéré, Thierry

    2014-05-01

    The overthickened crust of the current Central Andes is commonly viewed as the result of tectonic shortening. However, in the present-day terrestrial forearc and arc of southwesternmost Peru, crustal thickness increases from 30 km along the coastline to >60 km below the active arc, whereas the upper crust exhibits little to no evidence of crustal shortening and, in constrast, many extensional features. How (and when) crustal overthickness was acquired in this region is thus little understood. Because crustal overthickening often results in extensional collapse and/or significant erosion, here we address this issue through a regional-scale study of exhumation using fission-track thermochronology. The limited fission-track data previously available in the area suggested that exhumation began during the Mesozoic. In this study, we present new apatite and zircon fission-track data obtained along the current terrestrial forearc of southwesternmost Peru. This relatively restricted area presents the interest of providing extensive outcrops of Precambrian to Ordovician basement and Early Jurassic to Late Cretaceous arc plutons. In order to compare the chronology of exhumation of these units, we performed extensive sampling for fission-track dating, as well as structural mapping. Our results indicate that the basement rocks and Jurassic plutons that crop out in the Arequipa region, where the crust is now >50 km-thick, experienced a rapid cooling through the 240-110°C temperature range between ~65 and ~35 Ma. This period of rapid exhumation coincided in time with the accumulation of terrestrial forearc deposits (the Lower Moquegua Group), that exhibit many syn-sedimentary extensional features and are bounded by conspicuous normal faults, specifically along the region where intense activity of the main arc between ~90 and ~60 Ma had led to voluminous magma emplacement. This close succession of (1) intense magmatic activity and (2) regional-scale exhumation associated with

  8. Lithologic discrimination of volcanic and sedimentary rocks by spectral examination of Landsat TM data from the Puma, Central Andes Mountains

    NASA Technical Reports Server (NTRS)

    Fielding, E. J.

    1986-01-01

    The Central Andes are widely used as a modern example of noncollisional mountain-building processes. The Puna is a high plateau in the Chilean and Argentine Central Andes extending southward from the altiplano of Bolivia and Peru. Young tectonic and volcanic features are well exposed on the surface of the arid Puna, making them prime targets for the application of high-resolution space imagery such as Shuttle Imaging Radar B and Landsat Thematic Mapper (TM). Two TM scene quadrants from this area are analyzed using interactive color image processing, examination, and automated classification algorithms. The large volumes of these high-resolution datasets require significantly different techniques than have been used previously for the interpretation of Landsat MSS data. Preliminary results include the determination of the radiance spectra of several volcanic and sedimentary rock units and the use of the spectra for automated classification. Structural interpretations have revealed several previously unknown folds in late Tertiary strata, and key zones have been targeted to be investigated in the field. The synoptic view of space imagery is already filling a critical gap between low-resolution geophysical data and traditional geologic field mapping in the reconnaissance study of poorly mapped mountain frontiers such as the Puna.

  9. Boron isotope composition of geothermal fluids and borate minerals from salar deposits (central Andes/NW Argentina)

    NASA Astrophysics Data System (ADS)

    Kasemann, Simone A.; Meixner, Anette; Erzinger, Jörg; Viramonte, José G.; Alonso, Ricardo N.; Franz, Gerhard

    2004-06-01

    We have measured the boron concentration and isotope composition of regionally expansive borate deposits and geothermal fluids from the Cenozoic geothermal system of the Argentine Puna Plateau in the central Andes. The borate minerals borax, colemanite, hydroboracite, inderite, inyoite, kernite, teruggite, tincalconite, and ulexite span a wide range of δ11B values from -29.5 to -0.3‰, whereas fluids cover a range from -18.3 to 0.7‰. The data from recent coexisting borate minerals and fluids allow for the calculation of the isotope composition of the ancient mineralizing fluids and thus for the constraint of the isotope composition of the source rocks sampled by the fluids. The boron isotope composition of ancient mineralizing fluids appears uniform throughout the section of precipitates at a given locality and similar to values obtained from recent thermal fluids. These findings support models that suggest uniform and stable climatic, magmatic, and tectonic conditions during the past 8 million years in this part of the central Andes. Boron in fluids is derived from different sources, depending on the drainage system and local country rocks. One significant boron source is the Paleozoic basement, which has a whole-rock isotopic composition of δ11B=-8.9±2.2‰ (1 SD); another important boron contribution comes from Neogene-Pleistocene ignimbrites ( δ11B=-3.8±2.8‰, 1 SD). Cenozoic andesites and Mesozoic limestones ( δ11B≤+8‰) provide a potential third boron source.

  10. Old transient landscapes and surface processes: Multiple cosmogenic nuclide and sediment yield data from the Central Andes of northern Chile

    NASA Astrophysics Data System (ADS)

    Kober, F.; Ivy-Ochs, S.; Schlunegger, F.; Zeilinger, G.; Kubik, P. W.; Baur, H.; Wieler, R.

    2005-12-01

    The desert parts of the Andes of northern Chile are regarded as being one of the oldest landscapes on Earth and hence landscape forming processes must act at very slow rates. These slow rates have promoted controversial ideas on the evolution of the Andean mountain chain and discussions whether climatic or tectonic forces predominate the geodynamic evolution of the Andes. Here we present erosion rates of hillslope interfluves across the slope of the western Central Andes (Arica area, northern Chile) derived from several long-lived terrestrial cosmogenic nuclides (10Be, 21Ne, 26Al). Erosion rates positively correlate with elevation and the historical precipitation record, suggesting a coupling between climate and erosion. In addition, it is suggested that the very old landscapes could be preserved in the western Central Andes thanks to low tectonic activity and the prevailing dry climate. Erosion rates estimated back into the middle to late Miocene are on the order of 10-100cm/My at the hyperarid Western Escarpment (Atacama Desert) and the Costal Cordillera. In contrast, erosion rates for the semiarid Western Cordillera are up to >3000cm/My, at least back into the Holocene/late Pleistocene. Here sediment yield data obtained on a decadal scale indicate denudation rates of a similar order of magnitude. In comparison, erosion rates obtained from long-lived cosmogenic nuclides on hillsope interfluves for the Western Cordillera and those derived from preliminary data (21Ne) on catchment wide erosion rates of the Lluta-drainage system yield similar orders of magnitudes. Additionally, catchment wide erosion rates remain largely constant throughout the entire catchment. The analyses of multiple terrestrial cosmogenic nuclides and the use of various "erosion-island" diagrams allowed the identification of system states and of possible complex exposure histories. Complex exposure was identified for non-bedrock samples, such as boulders or amalgamated clast samples. Cosmogenic

  11. Paleozoic evolution of active margin basins in the southern Central Andes (northwestern Argentina and northern Chile)

    NASA Astrophysics Data System (ADS)

    Bahlburg, H.; Breitkreuz, C.

    The geodynamic evolution of the Paleozoic continental margin of Gondwana in the region of the southern Central Andes is characterized by the westward progression of orogenic basin formation through time. The Ordovician basin in the northwest Argentinian Cordillera Oriental and Puna originated as an Early Ordovician back-arc basin. The contemporaneous magmatic arc of an east-dipping subduction zone was presumably located in northern Chile. In the back-arc basin, a ca. 3500 meter, fining-up volcaniclastic apron connected to the arc formed during the Arenigian. Increased subsidence in the late Arenigian allowed for the accomodation of large volumes of volcaniclastic turbidites during the Middle Ordovician. Subsidence and sedimentation were caused by the onset of collision between the para-autochthonous Arequipa Massif Terrane (AMT) and the South American margin at the Arenigian-Llanvirnian transition. This led to eastward thrusting of the arc complex over its back-arc basin and, consequently, to its transformation into a marine foreland basin. As a result of thrusting in the west, a flexural bulge formed in the east, leading to uplift and emergence of the Cordillera Oriental shelf during the Guandacol Event at the Arenigian-Llanvirnian transition. The basin fill was folded during the terminal collision of the AMT during the Oclóyic Orogeny (Ashgillian). The folded strata were intruded post-tectonically by the presumably Silurian granitoids of the "Faja Eruptiva de la Puna Oriental." The orogeny led to the formation of the positive area of the Arco Puneño. West of the Arco Puneño, a further marine basin developed during the Early Devonian, the eastern shelf of which occupied the area of the Cordillera Occidental, Depresión Preandina, and Precordillera. The corresponding deep marine turbidite basin was located in the region of the Cordillera de la Costa. Deposition continued until the basin fill was folded in the early Late Carboniferous Toco Orogeny. The basin

  12. Population genetic structure of traditional populations in the Peruvian Central Andes and implications for South American population history.

    PubMed

    Cabana, Graciela S; Lewis, Cecil M; Tito, Raúl Y; Covey, R Alan; Cáceres, Angela M; Cruz, Augusto F De La; Durand, Diana; Housman, Genevieve; Hulsey, Brannon I; Iannacone, Gian Carlo; López, Paul W; Martínez, Rolando; Medina, Ángel; Dávila, Olimpio Ortega; Pinto, Karla Paloma Osorio; Santillán, Susan I Polo; Domínguez, Percy Rojas; Rubel, Meagan; Smith, Heather F; Smith, Silvia E; Massa, Verónica Rubín de Celis; Lizárraga, Beatriz; Stone, Anne C

    2014-01-01

    Molecular-based characterizations of Andean peoples are traditionally conducted in the service of elucidating continent-level evolutionary processes in South America. Consequently, genetic variation among "western" Andean populations is often represented in relation to variation among "eastern" Amazon and Orinoco River Basin populations. This west-east contrast in patterns of population genetic variation is typically attributed to large-scale phenomena, such as dual founder colonization events or differing long-term microevolutionary histories. However, alternative explanations that consider the nature and causes of population genetic diversity within the Andean region remain underexplored. Here we examine population genetic diversity in the Peruvian Central Andes using data from the mtDNA first hypervariable region and Y-chromosome short tandem repeats among 17 newly sampled populations and 15 published samples. Using this geographically comprehensive data set, we first reassessed the currently accepted pattern of western versus eastern population genetic structure, which our results ultimately reject: mtDNA population diversities were lower, rather than higher, within Andean versus eastern populations, and only highland Y-chromosomes exhibited significantly higher within-population diversities compared with eastern groups. Multiple populations, including several highland samples, exhibited low genetic diversities for both genetic systems. Second, we explored whether the implementation of Inca state and Spanish colonial policies starting at about ad 1400 could have substantially restructured population genetic variation and consequently constitute a primary explanation for the extant pattern of population diversity in the Peruvian Central Andes. Our results suggest that Peruvian Central Andean population structure cannot be parsimoniously explained as the sole outcome of combined Inca and Spanish policies on the region's population demography: highland populations

  13. Climatic and paleoclimatic forcing of erosion in the southern Central Andes and the northwestern Himalaya (Invited)

    NASA Astrophysics Data System (ADS)

    Bookhagen, B.; Strecker, M. R.

    2013-12-01

    The windward flanks of the tectonically active southern Central Andes and the NW Himalaya are characterized by steep climatic, tectonic, and topographic gradients. The first windward topographic rise of these mountain ranges constitutes a significant orographic barrier resulting in high orographic rainfall causing some of the wettest places on Earth. However, the higher-elevation areas of the windward flanks of both regions become progressively drier, until arid conditions are attained in the orogen interiors (i.e., the Altiplano-Puna and Tibet plateaus). Both areas have experienced significant paleoclimatic changes with deeper penetration of moisture into the orogen and thus an orogenward shift of the climate gradient. Some of the world's largest rivers with high sediment loads emerge from these mountain belts, and understanding the relation between climate and erosion is key in predicting mass fluxes, assessing the impacts of climate variability, and long-term climate forcing of erosion on landscape evolution. Here, we quantify the impact of the climatic gradients and their spatial shifts during the late Pleistocene and Holocene. We rely on sedimentary archives, digital topography, and cosmogenic inventories of river sands (10Be) and bedrock-erosion rates (10Be and 26Al) from the Puna Plateau in NW Argentina and the interior of the western Himalaya in NW India. We make three key observations that underline the importance of present-day climatic parameters and paleoclimatic changes on the effiency of surface processes in both areas: (1) First-order spatial erosion patterns follow the climatic gradient and catchment-mean erosion rates vary by three orders of magnitude from the wet mountain fronts to the dry orogen interior. In NW Argentina, our measurements represent the fluvial transport rates and indicate very low fluvial activity in the interior of the Puna Plateau during the Late Pleistocene; (2) the spatial distribution of erosion rates can be explained by a

  14. Cold episodes in the Peruvian Central Andes: Composites, Types, and their Impacts over South America (1958-2014)

    NASA Astrophysics Data System (ADS)

    Sulca, J. C.; Vuille, M. F.; Roundy, P. E.; Trasmonte, G.; Silva, Y.; Takahashi, K.

    2015-12-01

    The Mantaro basin (MB) is located in the central Peruvian Andes. Occasionally, cold episodes are observed during austral summer (January-March), that strongly damage crops. However, little is known about the causes and impacts of such cold episodes. The main goal of this study is thus to characterize cold episodes in the MB and assess their large-scale circulation and teleconnections over South America (SA) during austral summer. To identify cold events in the MB daily minimum temperature (Tmin) for the period 1958-2014 from Huayao station, located within the MB was used. A cold episode is defined when daily minimum temperature drops below its 10-percentile for at least one day. Additionally, to study the sensitivity between physical mechanisms associated with cold episodes and temperature, cold episodes are classified in three groups: Weak cold episodes (7.5 ≤ Tmin ≤ 10 percentile), strong cold episodes (Tmin ≤ 2.5 percentile), but excluding the 9 coldest events (Tmin ≤ 0 ͦ C), henceforth referred to as extraordinary cold episodes. Several gridded reanalysis were used to characterize the large-scale circulation, cloud cover and rainfall over SA associated with these events. Weak and strong cold episodes in the MB are mainly associated with a weakening of the Bolivian High-Nordeste Low system by tropical-extratropical interactions. Both types of cold episodes are associated with westerly wind anomalies at mid- and upper-tropospheric levels aloft the Peruvian Central Andes, which inhibit the influx of humid air masses from the lowlands to the east and hence limit the development of cloud cover (e.g., positive OLR anomalies over MB). The resulting clear sky conditions cause nighttime temperatures to drop, leading to cold extremes below 10-percentile. Simultaneously, northeastern Brazil (NEB) registers negative OLR anomalies, strong convection and enhanced cloud cover because displacement of the South Atlantic Convergence Zone (SACZ) toward the northeast of

  15. Active tectonics of the Atacama Basin area, northern Chile: Implications for distribution of convergence across the central Andes

    NASA Astrophysics Data System (ADS)

    Chuang, Yi-Rung; Lin, Yen-Sheng; Shyu, J. Bruce H.

    2013-04-01

    The central Andes in South America is formed as the Nazca plate subducts northeastward beneath the South American plate along the Peru-Chile trench, parallel to the coastline. It has been shown that the convergence rate between the two plates is ~70-80 mm/yr, and about 10-15 mm/yr of the convergence is absorbed in the sub-Andean belt, east of the active volcanic arc. However, the convergence in the forearc region is still not well constrained. In order to understand how much convergence is absorbed in the forearc region, we analyzed the active tectonic characteristics of the Atacama Basin, just west of the active volcanic arc. With the help of various remote sensing datasets such as 30-m and 90-m resolution digital elevation models (DEM) produced from SRTM data, thermal infrared radiometer (TIR) ASTER images, Landsat, and Google Earth images, we identified many N-S trending compressional structures around the Atacama Basin. The active structures are found mainly in the northern and southern part of the basin. The structures in the north deformed many volcanic rocks at the surface, such as ignimbrites and several lava flows. Structures may extend southward to San Pedro de Atacama, the largest town in the Atacama Basin, and produced tectonic scarps inside the town. River terraces also formed in the hanging-wall block of the structures, north of San Pedro. From field surveys, we measured the offset amount of the structures and collected volcanic rocks in order to constrain the age of the deformation. These results enabled us to calculate the long-term deformation rate of the structures. Our results indicate that the long-term slip rate of the structures in the southern part of the basin is quite low, in the order of 10-1 mm/yr. Furthermore, we obtained detailed topographic profiles across the structures. In the south, the profiles were surveyed by using real-time kinematic (RTK) GPS. Together with the attitudes of bedding planes, we constructed the subsurface geometry

  16. Spatiotemporal variability of modern precipitation δ18O in the central Andes and implications for paleoclimate and paleoaltimetry estimates

    NASA Astrophysics Data System (ADS)

    Fiorella, Richard P.; Poulsen, Christopher J.; Pillco Zolá, Ramiro S.; Barnes, Jason B.; Tabor, Clay R.; Ehlers, Todd A.

    2015-05-01

    Understanding the patterns of rainfall isotopic composition in the central Andes is hindered by sparse observations. Despite limited observational data, stable isotope tracers have been commonly used to constrain modern-to-ancient Andean atmospheric processes, as well as to reconstruct paleoclimate and paleoaltimetry histories. Here, we present isotopic compositions of precipitation (δ18Op and δDp) from 11 micrometeorological stations located throughout the Bolivian Altiplano and along its eastern flank at ~21.5°S. We collected and isotopically analyzed 293 monthly bulk precipitation samples (August 2008 to April 2013). δ18Op values ranged from -28.0‰ to 9.6‰, with prominent seasonal cycles expressed at all stations. We observed a strong relationship between the δ18Op and elevation, though it varies widely in time and space. Constraints on air sourcing estimated from atmospheric back trajectory calculations indicate that continental-scale climate dynamics control the interannual variability in δ18Op, with upwind precipitation anomalies having the largest effect. The impact of precipitation anomalies in distant air source regions to the central Andes is in turn modulated by the Bolivian High. The importance of the Bolivian High is most clearly observed on the southern Bolivian Altiplano. However, monthly variability among Altiplano stations can exceed 10‰ in δ18Op on the plateau and cannot be explained by elevation or source variability, indicating a nontrivial role for local scale effects on short timescales. The strong influence of atmospheric circulation on central Andean δ18Op requires that paleoclimate and paleoaltimetry studies consider the role of South American atmospheric paleocirculation in their interpretation of stable isotopic values as proxies.

  17. Changes in maximum and minimal temperatures at high elevation stations in the central Andes of South America

    SciTech Connect

    Quintana-Gomez, R.A.

    1997-11-01

    Temperature trends and deviations were evaluated for the central Andes portion of Bolivia. Data were collected primarily from stations located at very high altitude (3,000 m above sea level and higher) for a 73-year period from 1918 to 1990. The analysis determined maximum and minimum temperature trends and the daily temperature range (DTR) at each station. The minimum temperature series showed a rather sustained increase starting in the 1960s and continuing to the present, and a reduction of the differential rate of warming for the same interval. The high elevation, rural area data appears to reinforce evidence of a global and generalized rise of minimum temperature and decrease of the DTR. 3 refs., 2 figs., 1 tab.

  18. GOCE satellite derived gravity and gravity gradient corrected for topographic effect in the South Central Andes region

    NASA Astrophysics Data System (ADS)

    Álvarez, Orlando; Gimenez, Mario; Braitenberg, Carla; Folguera, Andres

    2012-08-01

    Global gravity field models, derived from satellite measurements integrated with terrestrial observations, provide a model of the Earth's gravity field with high spatial resolution and accuracy. The Earth Gravity Model EGM08, a spherical harmonic expansion of the geopotential up to degree and order 2159, has been used to calculate two functionals of the geopotential: the gravity anomaly and the vertical gravity gradient applied to the South Central Andes area. The satellite-only field of the highest resolution has been developed with the observations of satellite GOCE, up to degree and order 250. The topographic effect, a fundamental quantity for the downward continuation and validation of satellite gravity gradiometry data, was calculated from a digital elevation model which was converted into a set of tesseroids. This data is used to calculate the anomalous potential and vertical gravity gradient. In the Southern Central Andes region the geological structures are very complex, but not well resolved. The processing and interpreting of the gravity anomaly and vertical gradients allow the comparison with geological maps and known tectonic structures. Using this as a basis, a few features can be clearly depicted as the contact between Pacific oceanic crust and the Andean fold and thrust belt, the seamount chains over the Oceanic Nazca Plate, and the Famatinian and Pampean Ranges. Moreover the contact between the Rio de la Plata craton and the Pampia Terrain is of great interest, since it represents a boundary that has not been clearly defined until now. Another great lineament, the Valle Fertil-Desaguadero mega-lineament, an expression of the contact between Cuyania and Pampia terranes, can also be clearly depicted. The authors attempt to demonstrate that the new gravity fields can be used for identifying geological features, and therefore serve as useful innovative tools in geophysical exploration.

  19. Geodynamical evolution of Central Andes at 24°S as inferred by magma composition along the Calama-Olacapato-El Toro transversal volcanic belt

    NASA Astrophysics Data System (ADS)

    Matteini, M.; Mazzuoli, R.; Omarini, R.; Cas, R.; Maas, R.

    2002-11-01

    Miocene to Recent volcanism on the Puna plateau (Central Andes) developed in three geological settings: (a) volcanic arc in the Western Cordillera (Miocene-Recent); (b) trans-arc along the main NW-SE transverse fault systems (Miocene); and (c) back-arc, mainly monogenic volcanic centres (Pliocene-Quaternary). We have studied the evolution of the arc-trans-arc volcanism along one of the most extensive transverse structures of Central Andes, the Calama-Olacapato-El Toro, at 24°S. Compositional variations from arc to trans-arc volcanism provide insights into petrogenesis and magma source regions. Puntas Negras and Rincon volcanic centres are arc-type and have typical calc-alkaline geochemical and Sr-Nd-Pb isotopic characteristics. East of the arc, lavas of the Tul-Tul, Del Medio and Pocitos complexes (TUMEPO) are heavy rare earth element-depleted and could be derived from 20-30% of partial melting of a lower crustal garnet-bearing metabasite. These liquids could be variably mixed with arc magmas at the base of the crust (MASH). This suggests important contributions from lower crustal sources to TUMEPO centres. Products at the Quevar and Aguas Calientes volcanic complexes to the east of TUMEPO show a prominent upper crustal signature (high 86Sr/ 87Sr, low 143Nd/ 144Nd) and could represent mixtures of 20-30% TUMEPO-type liquids with up to 70-80% of upper crustal melts. We propose a geodynamic model to explain geochemical variations for the arc-trans-arc transverse volcanism from the Upper Miocene to Recent. In our model, arc volcanism is linked to dehydration of the subducting Nazca plate, which produces typical calc-alkaline compositions. During the Upper Miocene (10-5 Ma), lithospheric evolution in the Puna plateau was dominated by thickening of ductile lower crust and thinning of the lithosphere. Lower crustal melting was promoted by concomitant asthenospheric upwelling and water release from the amphibolite-eclogite transformation, yielding TUMEPO magmas with lower

  20. A first shallow firn-core record from Glaciar La Ollada, Cerro Mercedario, central Argentine Andes

    NASA Astrophysics Data System (ADS)

    Bolius, David; Schwikowski, Margit; Jenk, Theo; Gäggeler, Heinz W.; Casassa, Gino; Rivera, Andrés

    In January 2003, shallow firn cores were recovered from Glaciar Esmeralda on Cerro del Plomo (33°14‧ S, 70°13‧ W; 5300 ma.s.l.), central Chile, and from Glaciar La Ollada on Cerro Mercedario (31°58‧ S, 70°07‧ W; 6070 ma.s.l.), Argentina, in order to find a suitable archive for paleoclimate reconstruction in a region strongly influenced by the El Niño-Southern Oscillation. In the area between 28° S and 35° S, the amount of winter precipitation is significantly correlated to the Southern Oscillation Index, with higher values during El Niño years. Glaciochemical analysis indicates that the paleo-record at Glaciar La Ollada is well preserved, whereas at Glaciar Esmeralda the record is strongly influenced by meltwater formation and percolation. A preliminary dating of the Mercedario core by annual-layer counting results in a time-span of 17 years (1986-2002), yielding an average annual net accumulation of 0.45 m w.e.

  1. The Vallenar Discontinuity and the Maipo Orocline: Regional significance of clockwise vertical-axis rotations in the central Chilean Andes.

    NASA Astrophysics Data System (ADS)

    Arriagada, C.; Roperch, P.; Mpodozis, C.; Charrier, R.; Yanez, G.; Farias, M.

    2009-05-01

    One of the most prominent tectonic features of the Andes is the Central Andean Rotation Pattern (CARP), which is closely related to the Bolivian Orocline and characterized by paleomagnetically determined clockwise rotations in northern Chile and counterclockwise rotations in southern Peru (Arriagada et al., 2008). Along the Chilean margin, between 29°S and 38°S, three prominent curvatures are observed. The Vallenar Discontinuity near ˜29°S corresponds to the southern limit of the Bolivian Orocline. North of 29°S the major structural elements (Paleozoic basement highs and thrusts) are NNE oriented while from 29°S down to 32°S the structures are mainly NS. The central Chilean margin presents also significant bends near Santiago (˜33°S, Maipo Orocline) and in the Arauco region (˜38°S). Near Santiago, the Maipo bend coincides with the subduction of the Juan Fernandez Ridge (JFR). During the last five years we have undertaken new paleomagnetic and structural studies along the forearc of northern and central Chile in order to understand the origin of the bends in the Chilean margin and the consequence of its indentation by the JFR. Clockwise rotations are, consistently large (30°S- 45°) north of the Vallenar discontinuity, but south of the Vallenar discontinuity, the segment between 29°S to 32°S was not subjected to significant clockwise rotation. South of ˜33°S, significant clockwise deflections up to 39° of the declinations are again observed. Rotations occur both in Mesozoic rocks of the Coastal Cordillera and Tertiary rocks of the Main Cordillera. Whereas most of the CARP rotations, involving bending of the Bolivian Orocline and clockwise rotations north of the Vallenar Discontinuity, occurred essentially during the Paleogene, the paleomagnetic rotations obtained in Tertiary formations of central Chile constrain the maximum possible age for the occurrence of rotations of the Maipo Orocline to the Miocene. Neogene shortening in the foreland belt

  2. Carbonatite diversity in the Central Andes: the Ayopaya alkaline province, Bolivia

    NASA Astrophysics Data System (ADS)

    Schultz, Frank; Lehmann, Bernd; Tawackoli, Sohrab; Rössling, Reinhard; Belyatsky, Boris; Dulski, Peter

    2004-12-01

    The Ayopaya province in the eastern Andes of Bolivia, 100 km NW of Cochabamba, hosts a Cretaceous alkaline rock series within a Palaeozoic sedimentary sequence. The alkaline rock association comprises nepheline-syenitic/foyaitic to ijolitic intrusions, carbonatite, kimberlite, melilititic, nephelinitic to basanitic dykes and diatremes, and a variety of alkaline dykes. The carbonatites display a wide petrographic and geochemical spectrum. The Cerro Sapo area hosts a small calciocarbonatite intrusion and a multitude of ferrocarbonatitic dykes and lenses in association with a nepheline-syenitic stock. The stock is crosscut by a spectacular REE-Sr-Th-rich sodalite-ankerite-baryte dyke system. The nearby Chiaracke complex represents a magnesiocarbonatite intrusion with no evidence for a relationship to igneous silicate rocks. The magnesiocarbonatite (Σ REE up to 1.3 wt%) shows strong HREE depletion, i.e. unusually high La/Yb ratios (520 1,500). Calciocarbonatites (Σ REE up to 0.5 wt%) have a flatter REE distribution pattern (La/Yb 95 160) and higher Nb and Zr contents. The sodalite-ankerite-baryte dyke system shows geochemical enrichment features, particularly in Na, Ba, Cl, Sr, REE, which are similar to the unusual natrocarbonatitic lavas of the recent volcano of Oldoinyo Lengai, Tanzania. The Cerro Sapo complex may be regarded as an intrusive equivalent of natrocarbonatitic volcanism, and provides an example for carbonatite genesis by late-stage crystal fractionation and liquid immiscibility. The magnesiocarbonatite intrusion of Chiaracke, on the other hand, appears to result from a primary carbonatitic mantle melt. Deep seated mantle magmatism/metasomatism is also expressed by the occurrence of a kimberlite dyke. Neodymium and strontium isotope data (ɛNd 1.4 5.4, 87Sr/86 Sr

  3. Cenozoic uplift of the Central Andes in northern Chile and Bolivia - reconciling paleoaltimetry with the geological evolution.

    NASA Astrophysics Data System (ADS)

    Lamb, S. H.

    2015-12-01

    The Cenozoic geological evolution of the Central Andes, along two transects between ~17.5°S and 21°S, is compared with paleo-topography, determined from published paleo-altimetry studies. Surface and rock uplift are quantified using simple 2-D models of crustal shortening and thickening, together with estimates of sedimentation, erosion and magmatic addition. Prior to ~25 Ma, during a phase of amagmatic flat-slab subduction, thick skinned crustal shortening and thickening was focused in the Eastern and Western Cordilleras, separated by a broad basin up to 300 km wide and close to sea level, which today comprises the high Altiplano. Surface topography in the Eastern Cordillera appears to be ~1 km lower than anticipated from crustal thickening, which may be due to the pull-down effect of the subducted slab, coupled to the overlying lithosphere by a cold mantle wedge. Oligocene steepening of the subducted slab is indicated by the initiation of the volcanic arc at ~27 - 25 Ma, and widespread mafic volcanism in the Altiplano between 25 and 20 Ma. This may have resulted in detachment of mantle lithosphere and possibly dense lower crust, triggering 1 - 1.5 km of rapid uplift (over << 5 Myrs) of the Altiplano and western margin of the Eastern Cordillera and establishing the present day lithospheric structure beneath the high Andes. Since ~25 Ma, surface uplift has been the direct result of crustal shortening and thickening, locally modified by the effects of erosion, sedimentation and magmatic addition from the mantle. The rate of crustal shortening and thickening varies with location and time, with two episodes of rapid shortening in the Altiplano, lasting < 5 Myrs, that are superimposed on a long term history of ductile shortening in the lower crust, driven by underthrusting of the Brazilian Shield on the eastern margin.

  4. Tectonic Evolution of the Central Andes during Mesozoic-Cenozoic times: Insights from the Salar de Atacama Basin

    NASA Astrophysics Data System (ADS)

    Peña Gomez, M. A.; Bascunan, S. A.; Becerra, J.; Rubilar, J. F.; Gómez, I.; Narea, K.; Martínez, F.; Arriagada, C.; Le Roux, J.; Deckart, K.

    2015-12-01

    The classic Salar de Atacama Basin, located in the Central Andes of northern Chile, holds a remarkable yet not fully understood record of tectonic events since mid-Cretaceous times. Based on the growing amount of data collected over the last years, such as high-detail maps and U-Pb geochronology, we present an updated model for the development of this area after the Triassic. A major compressional event is recorded around the mid-Late Cretaceous (ca. 107 Ma) with the deposition of synorogenic continental successions reflecting the uplift of the Coastal Cordillera area farther to the west, and effectively initiating the foreland basin. The deformation front migrated eastwards during the Late Campanian (ca. 79 Ma), where it exhumed and deformed the Late Cretaceous magmatic arc and the crystalline basement of Cordillera de Domeyko. The K-T Event (ca. 65 Ma), recently identified in the basin, involved the same source areas, though the facies indicate a closer proximity to the source. The compressional record of the basin is continued by the Eocene Incaic Event (ca. 45 Ma), with deep exhumation of the Cordillera de Domeyko and the cannibalization of previous deposits. A change to an extensional regime during the Oligocene (ca. 28 Ma) is shown by the deposition of more than 4 km of evaporitic and clastic successions. A partial inversion of the basin occurred during the Miocene (ca.10 Ma-present), as shown by the deformation seen in the Cordillera de la Sal. As such, the basin shows that the uplift of the Cordillera de Domeyko was not one isolated episode, but a prolonged and complex event, punctuated by episodes of major deformation. It also highlights the need to take into account the Mesozoic-Cenozoic deformation events for any model trying to explain the building of the modern-day Andes.

  5. The Quebradagrande Complex: A Lower Cretaceous ensialic marginal basin in the Central Cordillera of the Colombian Andes

    NASA Astrophysics Data System (ADS)

    Nivia, Alvaro; Marriner, Giselle F.; Kerr, Andrew C.; Tarney, John

    2006-09-01

    The Quebradagrande Complex of Western Colombia consists of volcanic and Albian-Aptian sedimentary rocks of oceanic affinity and outcrops in a highly deformed zone where spatial relationships are difficult to unravel. Berriasian-Aptian sediments that display continental to shallow marine sedimentary facies and mafic and ultramafic plutonic rocks are associated with the Quebradagrande Complex. Geochemically, the basalts and andesites of the Quebradagrande Complex mostly display calc-alkaline affinities, are enriched in large-ion lithophile elements relative to high field strength elements, and thus are typical of volcanic rocks generated in supra-subduction zone mantle wedges. The Quebradagrande Complex parallels the western margin of the Colombian Andes' Central Cordillera, forming a narrow, discontinuous strip fault-bounded on both sides by metamorphic rocks. The age of the metamorphic rocks east of the Quebradagrande Complex is well established as Neoproterozoic. However, the age of the metamorphics to the west - the Arquía Complex - is poorly constrained; they may have formed during either the Neoproterozoic or Lower Cretaceous. A Neoproterozoic age for the Arquía Complex is favored by both its close proximity to sedimentary rocks mapped as Paleozoic and its intrusion by Triassic plutons. Thus, the Quebradagrande Complex could represent an intracratonic marginal basin produced by spreading-subsidence, where the progressive thinning of the lithosphere generated gradually deeper sedimentary environments, eventually resulting in the generation of oceanic crust. This phenomenon was common in the Peruvian and Chilean Andes during the Uppermost Jurassic and Lower Cretaceous. The marginal basin was trapped during the collision of the Caribbean-Colombian Cretaceous oceanic plateau, which accreted west of the Arquía Complex in the Early Eocene. Differences in the geochemical characteristics of basalts of the oceanic plateau and those of the Quebradagrande Complex

  6. A glassy lava flow from Toconce volcano and its relation with the Altiplano-Puna Magma Body in Central Andes

    NASA Astrophysics Data System (ADS)

    Godoy, B.; Rodriguez, I.; Aguilera, F.

    2012-12-01

    Toconce is a composite stratovolcano located at the San Pedro - Linzor volcanic chain (SPLVC). This volcanic chain distributes within the Altiplano-Puna region (Central Andes) which is characterized by extensive rhyodacitic-to-rhyolitic ignimbritic fields, and voluminous domes of dacitic-to-rhyolitic composition (de Silva, 1989). The felsic melts that gave origin to ignimbrites and domes at this area were generated by mixing of mantle-derived magmas and anatectic melts assimilated during their ascent through the thick crust. Thus, partially molten layers exist in the upper crust below the APVC (de Silva et al., 2006). Evidence of large volumes of such melts has been also proposed by geophysical methods (i.e. the Altiplano-Puna Magma Body; Chmielowsky et al., 1999) In this work, petrography and whole rock, mineralogical and melt inclusions geochemistry of a glassy lava flow of Toconce volcano are presented. Petrographically, this lava flow shows a porphyric texture, with euhdral to subhedral plagioclase, ortho- and clino-pyroxene phenocrysts immersed in a glassy groundmass. Geochemically, the lava flow has 64.7% wt. SiO2. The glassy groundmass (~70% wt. SiO2) is more felsic than all the lavas in the volcanic chain (47-68% wt., Godoy et al., 2011). Analyzed orthopyroxene-hosted melt inclusions show an even higher SiO2 content (72-75% wt.), and a decreasing on Al2O3, Na2O, and CaO content with differentiation. Crystallization pressures of this lava flow, obtained using Putirka's two-pyroxene and clinopyroxene-liquid models (Putirka, 2008), range between 6 and 9 kbar. According to crystallization pressures, and major element composition, a felsic source located at shallow crustal pressures - where plagioclase is a stable mineralogical phase - originated the inclusions. This could be related to the presence of the Altiplano-Puna Magma Body (APMB) located below SPLVC. On the other hand, glassy groundmass, and disequilibrium textures in minerals of this lava flow could

  7. Historical Glacier Variations in Southern South America since the Little Ice Age: Examples from Lago Viedma (Southern Patagonia) and Mendoza (Central Andes), Argentina

    NASA Astrophysics Data System (ADS)

    Nussbaumer, S. U.; Masiokas, M.; Pitte, P.; Berthier, E.; Guerrido, C.; Luckman, B. H.; Villalba, R.

    2013-12-01

    The evaluation of historical information can give valuable insight into past glacier dynamics, especially before the onset of modern measurements. Early photographs and maps depict changes for selected glaciers in southern South America. Within this study, written documents and pictorial historical records (drawings, sketches, engravings, photographs, chronicles, topographic maps) are analysed critically, with a particular focus on two regions: Lago Viedma (El Chaltén, southern Patagonia, 49.5°S, 73.0°W) and the Río Mendoza basin (Mendoza, central Andes, 33.1°S, 69.9°W). For the Lago Viedma area, early historical data for the end of the 19th century stem from the expedition of the Chilean-Argentinean border commission. In addition, the expedition by the German Scientific Society, conducted between 1910 and 1916, and the later photographs by Alberto M. de Agostini give an excellent depiction of the glaciers. Glaciar Viedma is a calving glacier which shows distinct retreat from 1896 until the present (though with a stationary or possibly advancing glacier front between 1930/31 and 1951/52), similar to the neighbouring glaciers. On the contrary, nearby Glaciar Perito Moreno shows an exceptional behaviour: the glacier front has been advancing during the first half of the 20th century, staying in an advanced position until the present. At the beginning of the 20th century, Robert Helbling explored the Argentinean-Chilean Andes together with his friend Friedrich Reichert. In the summer of 1909/10, they started a detailed survey of the highly glacierized Juncal-Tupungato mountains (Río Mendoza basin), leading to the first accurate topographic map of the area published in 1914. Its outstanding quality allows a comparison with contemporary satellite imagery. The area received attention in 1934, when the sudden drainage of a glacier-dammed lake in the upper Río del Plomo valley caused fatalities and considerable damage to constructions and the Transandine Railway. A

  8. The ash deposits of the 4200 BP Cerro Blanco eruption: the largest Holocene eruption of the Central Andes

    NASA Astrophysics Data System (ADS)

    Fernandez-Turiel, Jose-Luis; Saavedra, Julio; Perez-Torrado, Francisco-Jose; Rodriguez-Gonzalez, Alejandro; Carracedo, Juan-Carlos; Lobo, Agustin; Rejas, Marta; Gallardo, Juan-Fernando; Osterrieth, Margarita; Carrizo, Julieta; Esteban, Graciela; Martinez, Luis-Dante; Gil, Raul-Andres; Ratto, Norma; Baez, Walter

    2015-04-01

    We present new data about a major eruption -spreading approx. 110 km3 ashes over 440.000 km2- long thought to have occurred around 4200 years ago in the Cerro Blanco Volcanic Complex (CBVC) in the Central Andes of NW Argentina (Southern Puna, 26°45' S, 67°45' W). This eruption may be the biggest during the past five millennia in the Central Volcanic Zone of the Andes, and possibly one of the largest Holocene eruptions in the world. Discrimination and correlation of pyroclastic deposits of this eruption of Cerro Blanco was conducted comparing samples of proximal (domes, pyroclastic flow and fall deposits) with distal ash fall deposits (up to 400 km from de vent). They have been characterized using optical and electron microscopy (SEM), X-ray diffraction, particle-size distribution by laser diffraction and electron microprobe and HR-ICP-MS with laser ablation for major and trace element composition of glass, feldspars and biotite. New and published 14C ages were calibrated using Bayesian statistics. An one-at-a-time inversion method was used to reconstruct the eruption conditions using the Tephra2 code (Bonadonna et al. 2010, https://vhub.org/resources/tephra2). This method allowed setting the main features of the eruption that explains the field observations in terms of thickness and grain size distributions of the ash fall deposit. The main arguments that justify the correlation are four: 1) Compositional coincidence for glass, feldspars, and biotite in proximal and distal materials; 2) Stratigraphic and geomorphological relationships, including structure and thickness variation of the distal deposits; 3) Geochronological consistency, matching proximal and distal ages; and 4) Geographical distribution of correlated outcrops in relation to the eruption centre at the coordinates of Cerro Blanco. With a magnitude of 7.0 and a volcanic explosivity index or VEI 7, this eruption of ~4200 BP at Cerro Blanco is the largest in the last five millennia known in the Central

  9. Bimodal volcanism in a tectonic transfer zone: Evidence for tectonically controlled magmatism in the southern Central Andes, NW Argentina

    NASA Astrophysics Data System (ADS)

    Petrinovic, I. A.; Riller, U.; Brod, J. A.; Alvarado, G.; Arnosio, M.

    2006-04-01

    This field-based and analytical laboratory study focuses on the genetic relationship between bimodal volcanic centres and fault types of an important tectonic transfer zone in the southern Central Andes, the NW-SE striking Calama-Olacapato-Toro (COT) volcanic belt. More specifically, tectono-magmatic relationships are examined for the 0.55 Ma Tocomar, the 0.78 Ma San Jerónimo and the 0.45 Ma Negro de Chorrillos volcanic centres in the Tocomar area (66°30 W-24°15 S). Structures of the COT volcanic belt, notably NW-SE striking strike-slip faults and NE-SW trending normal faults, accommodated differential shortening between major N-S striking thrust faults on the Puna Plateau. We present evidence that bimodal volcanism was contemporaneous with activity of these fault types in the COT volcanic belt, whereby eruption and composition of the volcanic rocks in the Tocomar and San Jerónimo-Negro de Chorrillos areas appear to have been controlled by the kinematics of individual faults. More specifically, rhyolitic centres such as the Tocomar are associated with normal faults, whereas shoshonitic-andesitic monogenetic volcanoes, e.g., the San Jerónimo and Negro de Chorrillos centres, formed at strike-slip dominated faults. Thus, the eruption of higher viscous rhyolite magmas appears to have been facilitated in tectonic settings characterized by horizontal dilation whereas ascent and effusive volcanic activity of less viscous and hot basaltic andesites to shoshonites were controlled by subvertical strike-slip faults. While the Tocomar rhyolites are interpreted to be derived from an anatectic crustal source, geochemical characteristics of the San Jerónimo and Negro de Chorrillos shoshonitic andesites are in agreement with a deeper source. This suggests that the composition of erupted volcanic rocks as well as their spatial distribution in the Tocomar area is controlled by the activity of specific fault types. Such volcano-tectonic relationships are also evident from older

  10. Compositional variations of ignimbrite magmas in the Central Andes over the past 26 Ma - A multivariate statistical perspective

    NASA Astrophysics Data System (ADS)

    Brandmeier, M.; Wörner, G.

    2016-10-01

    Multivariate statistical and geospatial analyses based on a compilation of 890 geochemical and ~ 1200 geochronological data for 194 mapped ignimbrites from the Central Andes document the compositional and temporal patterns of large-volume ignimbrites (so-called "ignimbrite flare-ups") during Neogene times. Rapid advances in computational science during the past decade led to a growing pool of algorithms for multivariate statistics for large datasets with many predictor variables. This study applies cluster analysis (CA) and linear discriminant analysis (LDA) on log-ratio transformed data with the aim of (1) testing a tool for ignimbrite correlation and (2) distinguishing compositional groups that reflect different processes and sources of ignimbrite magmatism during the geodynamic evolution of the Central Andes. CA on major and trace elements allows grouping of ignimbrites according to their geochemical characteristics into rhyolitic and dacitic "end-members" and to differentiate characteristic trace element signatures with respect to Eu anomaly, depletions in middle and heavy rare earth elements (REE) and variable enrichments in light REE. To highlight these distinct compositional signatures, we applied LDA to selected ignimbrites for which comprehensive datasets were available. In comparison to traditional geochemical parameters we found that the advantage of multivariate statistics is their capability of dealing with large datasets and many variables (elements) and to take advantage of this n-dimensional space to detect subtle compositional differences contained in the data. The most important predictors for discriminating ignimbrites are La, Yb, Eu, Al2O3, K2O, P2O5, MgO, FeOt, and TiO2. However, other REE such as Gd, Pr, Tm, Sm, Dy and Er also contribute to the discrimination functions. Significant compositional differences were found between (1) the older (> 13 Ma) large-volume plateau-forming ignimbrites in northernmost Chile and southern Peru and (2) the

  11. Tertiary tectonics of the sub-Andean region of the North Patagonian Andes, southern central Andes of Argentina (41 42°30‧S)

    NASA Astrophysics Data System (ADS)

    Giacosa, Raúl E.; Afonso, Juan C.; Heredia C., Nemesio; Paredes, José

    2005-12-01

    The sub-Andean region of the North Patagonian Andes is located between the north Patagonian foreland and the highest elevations of the Andean Cordillera. Its Tertiary contractional structure, active since the upper Late Oligocene and through the upper Late Miocene, corresponds to the external sector of the North Patagonian Andes fold-and-thrust belt, which is characterized by east-vergent thrusts that affect stratified Cenozoic rocks. The units involved in the deformation correspond to El Maitén Oligocene volcanic belt, deformed between east-vergent thrusts and backthrusts, and Oligocene-Miocene sedimentary rocks of the Ñirihuau-Collón Curá Basin. The northern sector of the basin was structured as a thin-skinned fold belt that comprises the Ñirihuau fold belt and a frontal sedimentary wedge. To the south, sedimentary depocenters are confined between medium- to high-angle reverse faults with evidence of basement structural control. In both cases, the general tectonosedimentary framework shows the youngest units toward the east, in agreement with the advance of the orogenic wedge. Most of the Ñirihuau-Collón Curá Basin infill fits a foreland basin system model. Some sectors of the basin show evidence of structural control by normal faults in the initial sedimentation stages. This early extensional regime might be associated with late phases of Oligocene volcanism. Extensional structures probably were partially reactivated during the upper Late Oligocene, as suggested by seismic data.

  12. Elevation-dependent changes in n-alkane δD and soil GDGTs across the South Central Andes

    NASA Astrophysics Data System (ADS)

    Nieto-Moreno, Vanesa; Rohrmann, Alexander; van der Meer, Marcel T. J.; Sinninghe Damsté, Jaap S.; Sachse, Dirk; Tofelde, Stefanie; Niedermeyer, Eva M.; Strecker, Manfred R.; Mulch, Andreas

    2016-11-01

    Surface uplift of large plateaus may significantly influence regional climate and more specifically precipitation patterns and temperature, sometimes complicating paleoaltimetry interpretations. Thus, understanding the topographic evolution of tectonically active mountain belts benefits from continued development of reliable proxies to reduce uncertainties in paleoaltimetry reconstructions. Lipid biomarker-based proxies provide a novel approach to stable isotope paleoaltimetry and complement authigenic or pedogenic mineral proxy materials, in particular outside semi-arid climate zones where soil carbonates are not abundant but (soil) organic matter has a high preservation potential. Here we present δD values of soil-derived n-alkanes and mean annual air temperature (MAT) estimates based on branched glycerol dialkyl glycerol tetraether (brGDGT) distributions to assess their potential for paleoelevation reconstructions in the southern central Andes. We analyzed soil samples across two environmental and hydrological gradients that include a hillslope (26-28°S) and a valley (22-24°S) transect on the windward flanks of Central Andean Eastern Cordillera in NW Argentina. Our results show that present-day n-alkane δD values and brGDGT-based MAT estimates are both linearly related with elevation and in good agreement with present-day climate conditions. Soil n-alkanes show a δD lapse rate (Δ (δD)) of - 1.64 ‰ / 100 m (R2 = 0.91, p < 0.01) at the hillslope transect, within the range of δD lapse rates from precipitation and surface waters in other tropical regions in the Andes like the Eastern Cordillera in Colombia and Bolivia and the Equatorial and Peruvian Andes. BrGDGT-derived soil temperatures are similar to monitored winter temperatures in the region and show a lapse rate of ΔT = - 0.51 °C / 100 m (R2 = 0.91, p < 0.01), comparable with lapse rates from in situ soil temperature measurements, satellite-derived land-surface temperatures at this transect, and

  13. Modern and long-term evaporation of central Andes surface waters suggests paleo archives underestimate Neogene elevations

    NASA Astrophysics Data System (ADS)

    Fiorella, Richard P.; Poulsen, Christopher J.; Pillco Zolá, Ramiro S.; Jeffery, M. Louise; Ehlers, Todd A.

    2015-12-01

    Central Andean paleoelevations reconstructed from stable isotope and paleofloral data imply a large magnitude (>2 km) Miocene-to-modern surface uplift. However, the isotopic relationships between precipitation, surface waters, and soil waters upon which these reconstructions are based remain poorly constrained for both past, and in many cases, modern conditions. We quantify the relationships between central Andean precipitation and surface waters by measuring the isotopic composition of 249 stream water samples (δ18O and δD) collected between April 2009 and October 2012. The isotopic compositions of stream waters match precipitation along the eastern flank. In contrast, Altiplano surface waters possess a lower δD-δ18O slope (4.59 vs ∼8 for meteoric waters) not observed in precipitation, which signals heavy isotope evaporative enrichment in surface waters. Paleoclimate models indicate that highly evaporative conditions have persisted on the plateau throughout Andean uplift, and that conditions may have been more evaporative when the Andes were lower. Thus, more ancient proxy materials may have a greater evaporative bias than previously recognized and paleoelevation reconstructions from stable isotope based central Andean plateau proxy materials likely overstate Miocene-to-present surface uplift. We propose Altiplano paleoelevations of 1-2 km at 24.5 Ma, 1.5-2.9 km by 11.45 Ma, and modern elevations by ∼6 Ma based on the lightest isotopic compositions observed in Altiplano proxy materials, which are least likely to be influenced by evaporation. These constraints limit total late-Miocene-to-modern uplift to <2.2 km, are more consistent with crustal shortening records, and suggest that plateau uplift may have been more spatially uniform than suggested by previous interpretations of stable isotope proxies.

  14. Zonda downslope winds in the central Andes of South America in a 20-year climate simulation with the Eta model

    NASA Astrophysics Data System (ADS)

    Antico, Pablo L.; Chou, Sin Chan; Mourão, Caroline

    2015-12-01

    The Zonda wind is a local version of the alpine foehn in the central Andes Mountains in South America. It blows on the eastern slopes and produces an extremely warm and dry condition in Argentina. In this study, the occurrence of Zonda wind events during a 20-year simulation from the regional Eta model is analyzed and results are compared to previous studies of Zonda wind events based on weather observations. We define a set of parameters to account for the zonal pressure gradient across the mountain, vertical movement, and air humidity typical of Zonda wind events. These parameters are applied to characterize Zonda wind events in model run and to classify them as surface-level or high-level episodes. The resulting annual distribution of Zonda occurrences based on composite analyses shows a preference for winter and spring with rare occurrences during summer. For the surface-level Zonda wind events, the highest frequency occurs during spring. Whereas surface-level Zonda wind episodes more commonly initiate in the afternoon, high-level Zonda wind events show no preference for a given initiation time. Our results are mostly in agreement with previous observational results.

  15. Cloud forest restoration for erosion control in a Kichwa community of the Ecuadorian central Andes Mountains

    NASA Astrophysics Data System (ADS)

    Backus, L.; Giordanengo, J.; Sacatoro, I.

    2013-12-01

    The Denver Professional Chapter of Engineers Without Borders (EWB) has begun conducting erosion control projects in the Kichwa communities of Malingua Pamba in the Andes Mountains south of Quito, Ecuador. In many high elevation areas in this region, erosion of volcanic soils on steep hillsides (i.e., < 40%) is severe and often associated with roads, water supply systems, and loss of native cloud forests followed by burning and cultivation of food crops. Following a 2011 investigation of over 75 erosion sites, the multidisciplinary Erosion Control team traveled to Malingua Pamba in October 2012 to conduct final design and project implementation at 5 sites. In partnership with the local communities, we installed woody cloud forest species, grass (sig-sig) contour hedges, erosion matting, and rock structures (toe walls, plunge pools, bank armoring, cross vanes, contour infiltration ditches, etc.) to reduce incision rates and risk of slump failures, facilitate aggradation, and hasten revegetation. In keeping with the EWB goal of project sustainability, we used primarily locally available resources. High school students of the community grew 5000 native trees and some naturalized shrubs in a nursery started by the school principal, hand weavers produced jute erosion mats, and rocks were provided by a nearby quarry. Where possible, local rock was harvested from landslide areas and other local erosion features. Based on follow up reports and photographs from the community and EWB travelers, the approach of using locally available materials installed by the community is successful; plants are growing well and erosion control structures have remained in place throughout the November to April rainy season. The community has continued planting native vegetation at several additional erosion sites. Formal monitoring will be conducted in October 2013, followed by analysis of data to determine if induced meandering and other low-maintenance erosion control techniques are working

  16. Investigating crustal contamination: a case study from the Bolivian Altiplano, Central Andes

    NASA Astrophysics Data System (ADS)

    McLeod, C. L.; Davidson, J. P.; Nowell, G.

    2010-12-01

    Claire McLeod*, Jon Davidson, Geoff Nowell 1 1 NCIET, Department of Earth Sciences, Durham University, Science Labs, Durham, DH1 3LE, UK. * Corresponding Author: c.l.mcleod@dur.ac.uk During ascent towards the earth’s surface primary basaltic magma sourced from the mantle has the potential to interact with overlying crustal rocks. This leads to overprinting of source characteristics. Quantifying the mechanisms and timescales of crustal assimilation by differentiating magmas is key to improving our understanding of mantle source geochemistry. It is widely accepted that eruptives at continental arcs e.g. the Andes are the products of fractional crystallisation combined with intra crustal assimilation (e.g. Davidson et al., 2005). However, direct evidence of this interaction between mantle magmas and crustal rocks and the nature of potential crustal contaminants is rarely preserved. This is largely due to homogenisation and recrystallisation of mantle melts in shallow upper crustal magma chambers. On the Bolivian Altiplano to the east of the active Andean volcanic arc, monogenetic volcanic centres have erupted plagioclase-hornblende phyric lavas which are hosts to a range of crustal xenoliths. Entrained xenoliths contain evidence for partial melting in the form of quenched anatectic melts (now glass). The compositions of these quenched crustal melts hold key information regarding how ascending magmas interact with surrounding crustal wall rocks and how in turn, the crust melts. Analyses of glasses for their major element (EMP), trace element (LA-ICPMS) and Sr isotopic composition (microdrill-TIMS) aim to improve our knowledge of mass transfer during crust-magma interaction and highlight the limitations of current models of crustal contamination which employ bulk rock compositions in calculations e.g. (EC)AFC modelling, DePoalo, 1981; Spera & Bohrson, 2001. References Davidson, J.P., Hora, J.M., Garrison, J.M. and Dungan, M.A., (2005). Crustal Forensics in Arc Magmas

  17. Phylogeny and biogeography of the New World siskins and goldfinches: rapid, recent diversification in the Central Andes.

    PubMed

    Beckman, Elizabeth J; Witt, Christopher C

    2015-06-01

    Time-calibrated molecular phylogenies can help us to understand the origins of the diverse and unique Andean avifauna. Previous studies have shown that the tempo of diversification differed between the Andes and adjacent lowland regions of South America. Andean taxa were found to have speciated more recently and to have avoided the decelerated diversification that is typical of Neotropical lowland clades. The South American siskins, a Pleistocene finch radiation, may typify this Andean pattern. We investigated the phylogenetic biogeography of all the New World siskins and goldfinches in new detail. To understand the specific role of the Andes in siskin diversification, we asked: (1) Was diversification faster in Andean siskin lineages relative to non-Andean ones? (2) Did siskin lineages move into and out of the Andes at different rates? We found that siskin lineages in the Andes had higher diversification rates and higher outward dispersal rates than siskin lineages outside the Andes. We conclude that páramo expansion and contraction in response to Pleistocene climatic cycles caused accelerated diversification and outward dispersal in Andean siskins. The younger average age of bird species in the Andes compared to lowland South America may be attributable to bursts of recent diversification in siskins and several other vagile, open-habitat clades.

  18. Phylogeny and biogeography of the New World siskins and goldfinches: rapid, recent diversification in the Central Andes.

    PubMed

    Beckman, Elizabeth J; Witt, Christopher C

    2015-06-01

    Time-calibrated molecular phylogenies can help us to understand the origins of the diverse and unique Andean avifauna. Previous studies have shown that the tempo of diversification differed between the Andes and adjacent lowland regions of South America. Andean taxa were found to have speciated more recently and to have avoided the decelerated diversification that is typical of Neotropical lowland clades. The South American siskins, a Pleistocene finch radiation, may typify this Andean pattern. We investigated the phylogenetic biogeography of all the New World siskins and goldfinches in new detail. To understand the specific role of the Andes in siskin diversification, we asked: (1) Was diversification faster in Andean siskin lineages relative to non-Andean ones? (2) Did siskin lineages move into and out of the Andes at different rates? We found that siskin lineages in the Andes had higher diversification rates and higher outward dispersal rates than siskin lineages outside the Andes. We conclude that páramo expansion and contraction in response to Pleistocene climatic cycles caused accelerated diversification and outward dispersal in Andean siskins. The younger average age of bird species in the Andes compared to lowland South America may be attributable to bursts of recent diversification in siskins and several other vagile, open-habitat clades. PMID:25796324

  19. Use of high-resolution satellite images for detection of geological structures related to Central Andes geothermal field, Chile.

    NASA Astrophysics Data System (ADS)

    Benavides-Rivas, C. L.; Soto-Pinto, C. A.; Arellano-Baeza, A. A.

    2014-12-01

    Central valley and the border with Argentina in the center, and in the fault system Liquiñe-Ofqui in the South of the country. High resolution images from the LANDSAT 8 satellite have been used to delineate the geological structures related to the potential geothermal reservoirs located at the northern end of the Southern Volcanic Zone of Chile. It was done by applying the lineament extraction technique, using the ADALGEO software, developed by [Soto et al., 2013]. These structures have been compared with the distribution of main geological structures obtained in the field. It was found that the lineament density increases in the areas of the major heat flux indicating that the lineament analysis could be a power tool for the detection of faults and joint zones associated to the geothermal fields. A lineament is generally defined as a straight or slightly curved feature in the landscape visible satellite image as an aligned sequence of pixel intensity contrast compared to the background. The system features extracted from satellite images is not identical to the geological lineaments that are generally determined by ground surveys, however, generally reflects the structure of faults and fractures in the crust. A temporal sequence of eight Landsat multispectral images of Central Andes geothermal field, located in VI region de Chile, was used to study changes in the configuration of the lineaments during 2011. The presence of minerals with silicification, epidotization, and albitization, which are typical for geothrmal reservoirs, was also identified, using their spectral characteristics, and subsequently corroborated in the field. Both lineament analysis and spectral analysis gave similar location of the reservoir, which increases reliability of the results.

  20. Early Cenozoic Shortening and Foreland Basin Sedimentation in the Marañon Fold-thrust Belt, Central Peruvian Andes

    NASA Astrophysics Data System (ADS)

    Jackson, L. J.; Carlotto, V.; Horton, B. K.; Rosell, L. N.

    2015-12-01

    The Marañon fold-thrust belt in the westernmost Andes of Peru has long been considered a robust signature of early Cenozoic shortening in the Andean orogenic belt. However, the structural details and potential records of coeval synorogenic sedimentation remain elusive. We report results from new geologic mapping (1:50,000), cross-section construction, and U-Pb geochronology for the Matucana-Ticlio region at 11-12°S along the Lima-La Oroya highway. Zircon U-Pb age data from volcanic rocks and clastic basin fill provide a maximum depositional age of ~43 Ma for a middle Eocene syndeformational unit that we identify as the Anta Formation, which overlies the Paleocene Casapalca Formation. Sedimentary lithofacies and unconformable relationships within the volcaniclastic Anta Formation reveal mixed fluvial, alluvial-fan, and volcanic depositional conditions during shortening accommodated by a NE-verging thrust/reverse fault and corresponding backthrust (here named the Chonta fault system). Our cross-section reconstruction and geochronological data indicate that the region is a critical, possibly unique, zone of the broader NE-directed Marañon fold-thrust belt where pre-Neogene synorogenic sediments and their associated structures are preserved. We interpret this combined structural and basin system as an Eocene-age (Incaic) frontal thrust belt and corresponding foredeep to wedge-top depozone in central Peru. As one of the better-constrained segments of the Marañon fold-thrust belt, this zone provides insight into potential linkages with elusive early Cenozoic (Incaic) structures and foreland basin fill of the Western Cordillera and Altiplano farther south in the central Andean plateau.

  1. The Calama-Olacapato-El Toro fault system in the Puna Plateau, Central Andes: Geodynamic implications and stratovolcanoes emplacement

    NASA Astrophysics Data System (ADS)

    Norini, Gianluca; Baez, Walter; Becchio, Raul; Viramonte, Jose; Giordano, Guido; Arnosio, Marcelo; Pinton, Annamaria; Groppelli, Gianluca

    2013-11-01

    The structural evolution of the Puna Plateau is characterized by the activity of both orogen-parallel and orogen-oblique faults. Understanding the possible relationship between these two structural styles, their geodynamic implications and the influence on the migration of magmas is important to get insights into the tectonic and magmatic evolution of the Central Andes. In this study, we present a structural analysis of the orogen-oblique Calama-Olacapato-El Toro fault system and the surrounding orogen-parallel thrust faults in the central-eastern Puna Plateau. Morphostructural analysis and field mapping reveal the geometry, kinematics and dynamics of the tectonic features in the studied area. We propose a three-dimensional geometrical reconstruction of the main fault planes showing their attitude and intersections at depth. The study indicates that the crust underwent simultaneous deformation along both the vertical transcurrent Calama-Olacapato-El Toro fault system and the low-angle thrust faults, and that the back-arc portion of the Calama-Olacapato-El Toro fault system developed as a transfer zone among the main N-striking thrusts. Our model considers that both orogen-parallel and orogen-oblique fault systems should be regarded as parts of the same tectonic system, accommodating crustal shortening of a thickened crust. The study suggests that the tectonic control on the magma and fluid circulation in the crust is mainly related to the geometry of the fault planes and the orientation of the stress field, with a previously unrecognized important role played by the orogen-parallel thrust faults on the emplacement of the stratovolcanoes.

  2. Impact of Santiago de Chile urban atmospheric pollution on anthropogenic trace elements enrichment in snow precipitation at Cerro Colorado, Central Andes

    NASA Astrophysics Data System (ADS)

    Cereceda-Balic, F.; Palomo-Marín, M. R.; Bernalte, E.; Vidal, V.; Christie, J.; Fadic, X.; Guevara, J. L.; Miro, C.; Pinilla Gil, E.

    2012-02-01

    Seasonal snow precipitation in the Andes mountain range is evaluated as an environmental indicator of the composition of atmospheric emissions in Santiago de Chile metropolitan area, by measuring a set of representative trace elements in snow samples by ICP-MS. Three late winter sampling campaigns (2003, 2008 and 2009) were conducted in three sampling areas around Cerro Colorado, a Central Andes mountain range sector NE of Santiago (36 km). Nevados de Chillán, a sector in The Andes located about 500 km south from the metropolitan area, was selected as a reference area. The experimental results at Cerro Colorado and Nevados de Chillán were compared with previously published data of fresh snow from remote and urban background sites. High snow concentrations of a range of anthropogenic marker elements were found at Cerro Colorado, probably derived from Santiago urban aerosol transport and deposition combined with the effect of mining and smelting activities in the area, whereas Nevados de Chillán levels roughly correspond to urban background areas. Enhanced concentrations in surface snow respect to deeper samples are discussed. Significant differences found between the 2003, 2008 and 2009 anthropogenic source markers profiles at Cerro Colorado sampling points were correlated with changes in emission sources at the city. The preliminary results obtained in this study, the first of this kind in the southern hemisphere, show promising use of snow precipitation in the Central Andes as a suitable matrix for receptor model studies aimed at identifying and quantifying pollution sources in Santiago de Chile.

  3. The geochemical variations of the upper cenozoic volcanism along the Calama Olacapato El Toro transversal fault system in central Andes (˜24°S): petrogenetic and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Matteini, M.; Mazzuoli, R.; Omarini, R.; Cas, R.; Maas, R.

    2002-02-01

    In this paper, we present new geochemical and Sr-Nd isotopic data for several Upper Miocene volcanic centres aligned along one of the most extensive transcurrent lineament in the Central Andes, the Calama-Olacapato-El Toro (COT). The transversal volcanic belt along COT is constituted by large composite volcanoes and a caldera structure; they are, from NW to SE, Puntas Negras, Rincon, Tul Tul, Del Medio and Pocitos (TUMEPO), Quevar Aguas Calientes and Tastil. In order to compare chemical data from the different centres along the COT transect, differentiation effects were minimised by using data extrapolated at 60% SiO2 with least-square regression method. In the western sector of the COT, the volcanic products of Puntas Negras and Rincon show relatively high K2O and 87Sr/86Sr and low Rb/Cs, Ta/Th, La/Yb, 143Nd/144Nd. To the east, the TUMEPO products have high Sr and 143Nd/144Nd, La/Yb and Ba/Rb and low Y, 87Sr/86Sr. In the easternmost COT sector, Quevar, Aguas Calientes and Tastil volcanic complexes exhibit low La/Yb, high87Sr/Sr86 and low 143Nd/144Nd. On the basis of these data, we propose a petrogenetic and geodynamical model for Central Andes at 24°S. In correspondence of Miocene-Quaternary volcanic arc (Puntas Negras and Rincon), the magmas inherited a calcalkaline signature partly modified by upper crustal and/or sediment assimilation. In the central eastern sector, melting, assimilation, storage and homogenisation (MASH) processes occurred at the base of a thickened crust. In this COT sector, TUMEPO products show an evident lower crust signature and could be considered representative for MASH derived magmas. In the easternmost sector, Quevar, Aguas Calientes and Tastil products could represent magmas generated by partial melting of underthrusted Brasilian shield and mixed with magmas derived by MASH processes.

  4. A GIS-based Spatial Analysis of Volcanoes in the Central Andes: Insights Into Factors Controlling Volcano Spacing.

    NASA Astrophysics Data System (ADS)

    Savant, S. S.; de Silva, S. L.

    2005-12-01

    Volcano spacing has received little attention since the mid-70's when studies undertaken by Vogt (1974; EPSL) and then Marsh (1979; J Geol) suggested a regular spacing of volcanoes in arcs that ranged from 50 to 75 km for different arcs. The spacing was thought to be influenced by the thickness of the lithosphere or gravitational (Rayleigh-Taylor) instabilities related to source layer thickness and viscosity respectively. We have revisited these ideas through a detailed study of volcano distribution in the Central Volcanic Zone (CVZ) of the Andes where volcano spacing was thought to be around 70 km. The CVZ was selected as it is the type example of continental arc volcanism, built on an extremely thick crust of up to 70 km. The availability of a comprehensive dataset describing the relative age, location, and geomorphic characteristics of each volcano (Volcanoes of the Central Andes, de Silva and Francis, 1990, Springer Verlag) made this a compelling case study. The ready availability of ARC GIS Geographic Information Systems software and the geospatial analysis tools therein, allowed a comprehensive spatial analysis of the volcanoes to be conducted. Of the 1,118 volcanoes of ages from 23Ma to active in the CVZ, we focused on the 106 active and potentially active large composite volcanoes that define the modern arc. These volcanoes are related in time and thus to a consistent set of tectonic factors. The frequency distribution of inter-volcano distances shows a peak frequency in the 10 - 30 km range (71%) with subordinate between 40-80 km (19%) and 80 - 120 km (10%). The characteristic spacing is thus much smaller than the characteristic spacing of 70 km found previously and is consistent with Baker (1974; EPSL). The primary cause appears to be clustering of volcanoes into groups. The density of volcanoes is variable along the arc with regularly spaced clusters of two to three volcanoes in northern and southern parts of the arc (13 r°S to 19 r°S and 24 r° to 27

  5. Photosynthetic responses of trees in high-elevation forests: comparing evergreen species along an elevation gradient in the Central Andes.

    PubMed

    García-Plazaola, José I; Rojas, Roke; Christie, Duncan A; Coopman, Rafael E

    2015-05-22

    Plant growth at extremely high elevations is constrained by high daily thermal amplitude, strong solar radiation and water scarcity. These conditions are particularly harsh in the tropics, where the highest elevation treelines occur. In this environment, the maintenance of a positive carbon balance involves protecting the photosynthetic apparatus and taking advantage of any climatically favourable periods. To characterize photoprotective mechanisms at such high elevations, and particularly to address the question of whether these mechanisms are the same as those previously described in woody plants along extratropical treelines, we have studied photosynthetic responses in Polylepis tarapacana Philippi in the central Andes (18°S) along an elevational gradient from 4300 to 4900 m. For comparative purposes, this gradient has been complemented with a lower elevation site (3700 m) where another Polylepis species (P. rugulosa Bitter) occurs. During the daily cycle, two periods of photosynthetic activity were observed: one during the morning when, despite low temperatures, assimilation was high; and the second starting at noon when the stomata closed because of a rise in the vapour pressure deficit and thermal dissipation is prevalent over photosynthesis. From dawn to noon there was a decrease in the content of antenna pigments (chlorophyll b and neoxanthin), together with an increase in the content of xanthophyll cycle carotenoids. These results could be caused by a reduction in the antenna size along with an increase in photoprotection. Additionally, photoprotection was enhanced by a partial overnight retention of de-epoxized xanthophylls. The unique combination of all of these mechanisms made possible the efficient use of the favourable conditions during the morning while still providing enough protection for the rest of the day. This strategy differs completely from that of extratropical mountain trees, which uncouple light-harvesting and energy-use during long

  6. Structural inheritance and selective reactivation in the central Andes: Cenozoic deformation guided by pre-Andean structures in southern Peru

    NASA Astrophysics Data System (ADS)

    Perez, Nicholas D.; Horton, Brian K.; Carlotto, Victor

    2016-03-01

    Structural, stratigraphic, and geochronologic constraints from the Eastern Cordillera in the central Andean plateau of southern Peru (14-15°S) demonstrate the existence and position of major pre-Andean structures that controlled the accumulation of Triassic synrift fill and guided subsequent Cenozoic deformation. The timing of initial clastic deposition of the Triassic Mitu Group is here constrained to ~ 242-233 Ma on the basis of detrital and volcanic zircon U-Pb geochronology. Regionally distinct provenance variations, as provided by U-Pb age populations from localized synrift accumulations, demonstrate Triassic erosion of multiple diagnostic sources from diverse rift-flank uplifts. Stratigraphic correlations suggest synchronous initiation of extensional basins containing the Mitu Group, in contrast with previous interpretations of southward rift propagation. Triassic motion along the NE-dipping San Anton normal fault accommodated up to 7 km of throw and hanging-wall deposition of a synrift Mitu succession > 2.5 km thick. The contrasting orientation of a non-reactivated Triassic normal fault suggests selective inversion of individual structures in the Eastern Cordillera was dependent on fault dip and strike. Selective preservation of a ~ 4 km thick succession of Carboniferous-Permian strata in the down-dropped San Anton hanging wall, beneath the synrift Mitu Group, suggests large-scale erosional removal in the uplifted footwall. Field and map observations identify additional pre-Andean thrust faults and folds attributed to poorly understood Paleozoic orogenic events preserved in the San Anton hanging wall. Selective thrust reactivation of normal and reverse faults during later compression largely guided Cenozoic deformation in the Eastern Cordillera. The resulting structural compartmentalization and across-strike variations in kinematics and deformation style highlight the influence of inherited Paleozoic structures and Triassic normal faults on the long

  7. Cenozoic foreland basin system in the central Andes of northwestern Argentina: Implications for Andean geodynamics and modes of deformation

    NASA Astrophysics Data System (ADS)

    Decelles, P. G.; Carrapa, B.; Horton, B. K.; Gehrels, G. E.

    2011-12-01

    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-Paraná 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.

  8. Photosynthetic responses of trees in high-elevation forests: comparing evergreen species along an elevation gradient in the Central Andes

    PubMed Central

    García-Plazaola, José I.; Rojas, Roke; Christie, Duncan A.; Coopman, Rafael E.

    2015-01-01

    Plant growth at extremely high elevations is constrained by high daily thermal amplitude, strong solar radiation and water scarcity. These conditions are particularly harsh in the tropics, where the highest elevation treelines occur. In this environment, the maintenance of a positive carbon balance involves protecting the photosynthetic apparatus and taking advantage of any climatically favourable periods. To characterize photoprotective mechanisms at such high elevations, and particularly to address the question of whether these mechanisms are the same as those previously described in woody plants along extratropical treelines, we have studied photosynthetic responses in Polylepis tarapacana Philippi in the central Andes (18°S) along an elevational gradient from 4300 to 4900 m. For comparative purposes, this gradient has been complemented with a lower elevation site (3700 m) where another Polylepis species (P. rugulosa Bitter) occurs. During the daily cycle, two periods of photosynthetic activity were observed: one during the morning when, despite low temperatures, assimilation was high; and the second starting at noon when the stomata closed because of a rise in the vapour pressure deficit and thermal dissipation is prevalent over photosynthesis. From dawn to noon there was a decrease in the content of antenna pigments (chlorophyll b and neoxanthin), together with an increase in the content of xanthophyll cycle carotenoids. These results could be caused by a reduction in the antenna size along with an increase in photoprotection. Additionally, photoprotection was enhanced by a partial overnight retention of de-epoxized xanthophylls. The unique combination of all of these mechanisms made possible the efficient use of the favourable conditions during the morning while still providing enough protection for the rest of the day. This strategy differs completely from that of extratropical mountain trees, which uncouple light-harvesting and energy-use during long

  9. Attenuation tomography in the western central Andes: A detailed insight into the structure of a magmatic arc

    NASA Astrophysics Data System (ADS)

    Haberland, Christian; Rietbrock, Andreas

    2001-06-01

    High-quality data from 1498 local earthquakes recorded by the PISCO '94 (Proyecto de Investigatión Sismológica de la Cordillera Occidental, 1994) and ANCORP '96 (Andean Continental Research Project, 1996) temporary seismological networks allowed the detailed determination of the three-dimensional (3-D) attenuation structure (Qp-1) beneath the recent magmatic arc in the western central Andes (20° to 24°S). Assuming a frequency-independent Qp-1 in a frequency band between 1 and 30 Hz, whole path attenuation (t*) was estimated from the amplitude spectra of the P waves using spectral ratios and a spectral inversion technique. The damped least squares inversion (tomography) of the data reveals a complex attenuation structure. Crust and mantle of the forearc and subducting slab are generally characterized by low attenuation (Qp > 1000). Crust and mantle beneath the magmatic arc show elevated attenuation. The strongest anomaly of extremely low Qp is found in the crust between 22° and 23°S beneath the recent volcanic arc (Qp < 100). N-S variations can be observed: The western flank of the crustal attenuation anomaly follows the curved course of the volcanic front. North of 21°S the attenuation is less developed. In the northern part of the study area the low-Qp zone penetrates in the forearc mantle down to the subducting slab. In the south a deeper zone of high attenuation is resolved between 23° and 24°S directly above the subducting slab. Low Qp in the mantle correlates with earthquake clusters. The strong crustal attenuation is confined to the distribution of young ignimbrites and silicic volcanism and is interpreted as a thermally weakened zone with partial melts. The attenuation pattern in the upper mantle might reflect the variable extent of the asthenosphere and maps variations of subduction-related hydration processes in the mantle wedge from slab-derived fluids.

  10. Erosion and Sediment Transport Across and Along Pronounced Topographic and Climatic Gradients: Examples from the Central Andes and Himalaya

    NASA Astrophysics Data System (ADS)

    Bookhagen, Bodo; Strecker, Manfred; Olen, Stephanie

    2016-04-01

    Moisture impinging on high topographic barriers results in effective orographic barriers. For example, the interaction of the Indian Monsoon with the southern Himalaya and the South American Monsoon System with the eastern central Andes result in some of the most efficient orographic barriers on Earth. The steep topographic gradients, the impact of focused rainfall along the southern and eastern flanks of the range, and the northward and westward shifts of rainfall during frequent intensified storm systems are responsible for an efficient erosional regime, with some of the highest known erosion rates. The spatiotemporal correlation between various topographic, tectonic, climatic, and exhumational phenomena in these regions has resulted in the formulation of models of possible long-term erosional and tectonic feedback processes that drive the lateral expansion and vertical growth of mountain belts. However, despite an increase in thermochronologic, cosmogenic radionuclide, and sedimentological datasets that help explain some underlying mechanisms, the true nature of these relationships is still unclear and controversies particularly exist concerning the importance of the different forcing factors that drive sediment transport on different time scales. Here, we synthesize and assess these controversies with observations from studies conducted perpendicular to and along strike of the orogens, and combine them with new basin-wide erosion-rate data from the Sutlej Valley in the NW Himalaya and from the southern central Andean Plateau (Puna) in NW Argentina. At first order and across strike, erosion rates based on cosmogenic nuclide inventories on river sands suggest a correlation with rainfall rates. But along-strike rainfall gradients in the Himalaya indicate additional moderating factors, such as vegetation. Leeward of the orographic barrier, fluvial erosion variability increases and erosion processes become more stochastic. Further leeward in the high-elevation and

  11. Constraining the Lithospheric Structure of the Central Andes Using P- and S- wave Receiver Functions

    NASA Astrophysics Data System (ADS)

    Ryan, J. C.; Beck, S. L.; Zandt, G.; Wagner, L. S.; Minaya, E.; Tavera, H.

    2014-12-01

    The Central Andean Plateau (CAP) has elevations in excess of 3 km, and is part of the Andean Cordillera that resulted in part from shortening along the western edge of South America as it was compressed between the subducting Nazca plate and underthrusting Brazilian cratonic lithosphere. We calculated P- and S-wave receiver functions for the Central Andean Uplift and Geodynamics of High Topography (CAUGHT) temporary deployment of broadband seismometers in the Bolivian orocline (12°-20°S) region to investigate crustal thickness and lithospheric structure. Migration of the receiver functions is done using common conversion point (CCP) stacks through a 3D shear velocity model from ambient noise tomography (Ward et al., 2013). The P- and S-wave receiver functions provide similar estimates of the depth to Moho under the CAP. Crustal thicknesses include 60-65 km thick crust underneath the Bolivian Altiplano, crust that varies from ~70 km to ~50 km underneath the Eastern Cordillera and Interandean zone, and thins to 50 to 40 km crust in the Subandes and the edge of the foreland. The variable crustal thickness of the Eastern Cordillera and Interandean zone ranges from >70 km associated with the Los Frailes volcanic field at 19°-20°S to ~55 km beneath the 6 km peaks of the Cordillera Real at ~16°S. From our S-wave receiver functions, that have no multiples that can interfere with deeper structure, we also identify structures below the Moho. Along a SW-NE line that runs near La Paz where we have our highest station density, the S-wave CCP receiver-function stacks show a strong negative polarity arrival at a depth of ~120 km from the eastern edge of the Altiplano to the Subandean zone. We suggest this may be a good candidate for the base of the CAP lithosphere. In addition, above this depth the mantle is strongly layered, suggesting that there is not a simple high velocity mantle lithosphere associated with the continental lithosphere underthrusting the Andean orogen

  12. Soil n-alkane δD and Branched GDGTs Distributions Track Elevation-induced Precipitation and Temperature Changes along the South Central Andes (Argentina)

    NASA Astrophysics Data System (ADS)

    Nieto-Moreno, V.; Rohrmann, A.; van der Meer, M.; S Sinninghe Damsté, J.; Sachse, D.; Tofelde, S.; Niedermeyer, E. M.; Strecker, M. R.; Mulch, A.

    2015-12-01

    Orogenic surface uplift and topographic evolution of tectonically active mountain belts exert a strong impact on climatic teleconnections and Earth surface processes, including changes in global atmospheric circulation patterns, erosion rates, distribution of biomes, and precipitation patterns. Hence, quantifying the driving processes shaping the evolution of topography in ancient and active orogens is required in order to disentangle the dynamic interactions and feedbacks among surface uplift, climate, erosion and sedimentation. The south central Andes of Argentina provide a particularly suitable setting to study the interplay between the tectonic and climatic evolution of an actively subduction orogen over short and long time-scales. We present δD values of soil-derived n-alkane and brGDGTs distributions to assess their suitability for paleoelevation reconstructions in the southern central Andes. We collected soil samples from two different environmental and hydrological gradients, across the hillslope (26-28°S) and along a river-valley (22-24°S) of two individual mountain ranges. δD n-alkane and brGDGTs distributions are both linearly related with elevation and may be used for paleoaltimetry studies along the windward flanks of the south central Andes. δD n-alkane and brGDGT-derived temperature lapse rates broadly follow regional lapse rates along steep orographic fronts. The observed lapse rates are lower than the annual mean values of satellite-derived temperatures but approach those of temperature loggers along each transect. Instead, δD n-alkane lapse rates are in line with regional stream-water data. These linear relationships along the windward slopes break down when entering the internally drained part of the Puna plateau. Our data document that δD n-alkane and brGDGTs distributions can be used over time scales relevant for paleoclimate/-altimetry reconstructions but also stress that such reconstructions require knowledge of the depositional

  13. Structures and crustal development of the central andes between 21° and 25°S

    NASA Astrophysics Data System (ADS)

    Reutter, K.-J.; Giese, P.; Götze, H.-J.; Scheuber, E.; Schwab, K.; Schwarz, G.; Wigger, P.

    The tectonics of the morphostructural units of the Central Andean segment between 21°S and 25°S are reviewed and their relation to the deep crustal structures, as far as known from geophysical research, is discussed. Special regard is given to the superposition of structures due to the stepwise eastward displacement of four arc systems subsequently developing on the continental margin during the Andean Cycle: (1) Lias — Early Cretaceous, (2) Mid-Cretaceous, (3) Latest Cretaceous — Eocene, and (4) Miocene — Holocene. Within these arc systems, three areas of main tectonic activity can be distinguished: The subduction zone and subduction complex, the magmatic arc, and the backarc region. The subduction complexes of the fossil stages are not preserved and the tectonic activity of the present subduction complex affects the continent only locally along the coast. The structures of the four magmatic arcs are exposed respectively in the Coastal Range, the Longitudnal Valley, the Chilean Precordillera, and in the broad area extending from the Preandean Depression to the western part of the Eastern Cordillera. Notwithstanding great structural differences between the individual arcs, there are common features such as the close reationship between deformation and magmatism, the incorporation of basement into fold and horst structures, and conjugate reverse fault systems. In the case of oblique subduction, longitudinal strike slip faulting, which may be left-handed (Atacama Fault of the Coastal Range) or right-handed (West Fissure of the Chilean Precordillera), follows the magmatic arc. In the backarc region, east vergent fold and thrust belts developed only in the stages 3 and 4. All the different arc stages seem to have contributed gradually to crustal thickening as there is a general development in these systems from ensialic marine conditions over an environment of continental lowlands to the present high plateau situation.

  14. Dynamics of a large, restless, rhyolitic magma system at Laguna del Maule, southern Andes, Chile

    USGS Publications Warehouse

    Singer, Brad S.; Andersen, Nathan L.; Le Mével, Hélène; Feigl, Kurt L.; DeMets, Charles; Tikoff, Basil; Thurber, Clifford H.; Jicha, Brian R.; Cardonna, Carlos; Córdova, Loreto; Gil, Fernando; Unsworth, Martyn J.; Williams-Jones, Glyn; Miller, Craig W.; Fierstein, Judith; Hildreth, Edward; Vazquez, Jorge A.

    2014-01-01

    Explosive eruptions of large-volume rhyolitic magma systems are common in the geologic record and pose a major potential threat to society. Unlike other natural hazards, such as earthquakes and tsunamis, a large rhyolitic volcano may provide warning signs long before a caldera-forming eruption occurs. Yet, these signs—and what they imply about magma-crust dynamics—are not well known. This is because we have learned how these systems form, grow, and erupt mainly from the study of ash flow tuffs deposited tens to hundreds of thousands of years ago or more, or from the geophysical imaging of the unerupted portions of the reservoirs beneath the associated calderas. The Laguna del Maule Volcanic Field, Chile, includes an unusually large and recent concentration of silicic eruptions. Since 2007, the crust there has been inflating at an astonishing rate of at least 25 cm/yr. This unique opportunity to investigate the dynamics of a large rhyolitic system while magma migration, reservoir growth, and crustal deformation are actively under way is stimulating a new international collaboration. Findings thus far lead to the hypothesis that the silicic vents have tapped an extensive layer of crystal-poor, rhyolitic melt that began to form atop a magmatic mush zone that was established by ca. 20 ka with a renewed phase of rhyolite eruptions during the Holocene. Modeling of surface deformation, magnetotelluric data, and gravity changes suggest that magma is currently intruding at a depth of ~5 km. The next phase of this investigation seeks to enlarge the sets of geophysical and geochemical data and to use these observations in numerical models of system dynamics.

  15. Magmatism and the Shallowing of the Chilean Flatslab in the Central Andes

    NASA Astrophysics Data System (ADS)

    Kay, S. M.

    2014-12-01

    The magmatic history of the flatslab region between the Central and Southern Andean volcanic zones reflects shallowing of the slab, lithospheric thinning, narrowing of the asthenospheric wedge, crustal thickening and forearc removal by subduction erosion. Newly revised contours on the northern margin of the modern flatslab (Mulcahy et al. 2014) show the flattest part extends from ~28° to 33°S and is bounded by Pleistocene volcanic activity. An eastward broadening of the magmatic arc began after 18 Ma as westward drift of South America accelerated, but the most distinctive retroarc magmatism occurred after near normal subduction of the southward drifting Juan Fernandez Ridge began at ~11 Ma and ended as magmatism ceased in the Pampean ranges, ~ 700 km east of the trench at ~4.7 Ma. Recent seismic work in the retroarc area indicate a ~60 km thick crust under the Precordillera fold-thrust belt with transitions at ~20 and ~40 km that are considered to be the top of crystalline basement and an eclogitic facies transition. Chemical constraints from ~15-7 Ma magmatic rocks suggest eclogization is related to crustal thickening over the shallowing slab in accord with field relations for major thrusting in the region by ~8-7 Ma. High Ba/Th ratios in <9 Ma volcanic rocks are interpreted to reflect phengite breakdown in the mantle wedge with the fluids facilitating eclogization of the lower crust. Evidence for mantle melt contributions in the magmas up until ~7 Ma comes from more primitive isotopic values in 1088-1251 Ma amphibolite and granulite facies xenoliths (eNd = 0 to -3; 87Sr/86Sr =704-0.710) than in Miocene volcanic rocks (eNd = 0-1.7; 0.70325-0.70345; zircon eHf ~ 0). From ~8 to 3 Ma, the active volcanic arc front near 28°S and 33°S was translated ~ 40-50 km eastward in a suspected response to forearc removal by subduction erosion. Given the position of the arc and distance to the trench, the same amount of forearc was likely removed in the intervening flatslab

  16. Paleomagnetism in the Precordillera of northern Chile (22°30'S): implications for the history of tectonic rotations in the Central Andes

    NASA Astrophysics Data System (ADS)

    Somoza, Rubén; Tomlinson, Andrew

    2002-01-01

    Widespread clockwise rotations in Mesozoic and Lower Tertiary rocks of northern Chile have been interpreted as the sum of two rotational events separated in time: an early rotation related to local deformation plus a late rotation related to wholesale rotation of northern Chile linked to Late Cenozoic oroclinal bending in the Central Andes. In this paper we report new paleomagnetic data from Cretaceous, upper Oligocene and Miocene sedimentary rocks in the Precordillera of northern Chile. The results suggest that all these rocks acquired their remanence at or close to the time of deposition. The lack of rotation in undeformed lower Miocene strata clearly indicates that clockwise rotations found in underlying, faulted and folded Cretaceous rocks were completed before the Late Cenozoic. Results from nearby localities in deformed upper Oligocene strata would argue for little (˜5°) rotation since the late Oligocene. Data from widely separated Miocene localities covering an area of about 5000 km 2 in the Calama basin strongly suggest that northern Chile did not undergo significant wholesale rotation during the Late Cenozoic. This, together with previous paleomagnetic evidence against Neogene rigid-body-like rotation of the southern Peruvian forearc, suggests that the curved shape of the Central Andean forearc was not significantly enhanced during the Late Cenozoic. By inference, all of the rotation in most Mesozoic and Lower Tertiary rocks of northern Chile was accomplished in the Cretaceous and/or Early Cenozoic, when the locus of deformation in the Central Andes was localized in the present forearc region.

  17. Stress patterns of the Plio-Quaternary brittle deformation along the Calama-Olacapato-El Toro Fault, Central Andes

    NASA Astrophysics Data System (ADS)

    Lanza, F.; Tibaldi, A.; Waite, G. P.; Corazzato, C.; Bonali, F.; Nardin, A.

    2012-04-01

    Understanding the geometry and kinematics of the major structures of an orogen is essential to elucidate its style of deformation, as well as its tectonic evolution. We describe the temporal and spatial changes in the state of stress of the trans-orogen area of the Calama-Olacapato-El Toro (COT) Fault Zone in the Central Andes, at about 24° S within the northern portion of the Puna Plateau between the Argentina-Chile border. The importance of the COT derives principally from the Quaternary-Holocene activity recognized on some segments, which may shed new light on its possible control on Quaternary volcanism and on the seismic hazard assessment of the area. Field geological surveys along with kinematic analysis and numerical inversion of ~ 280 new fault-slip measurements have revealed that this portion of the COT consists mainly of NW-SE striking faults, which have been reactivated under three different kinematic regimes: 1) a Miocene transpressional phase with the maximum principal stress (σ1) chiefly trending NW-SE; 2) an extensional phase that started by 9 Ma, with a horizontal NW-SE-trending minimum principal stress (σ3) - permutations between σ2 and σ3 axes have been recognized at three sites - and 3) a left-lateral strike-slip phase with an ~ ENE-WSW σ1 and a ~ NNW-SSE σ3 dating to the late Pliocene-Quaternary. Spatially, in the Quaternary, the left-lateral component decreases toward the westernmost tip of the COT, where it transitions to extension; this produced to a N-S horst and graben structure. Hence, even if trascurrence is still active in the eastern portion of the COT, as focal mechanisms of crustal earthquakes indicate, our study demonstrates that extension is becoming the predominant structural style of deformation, at least in the western region. These major temporal and spatial changes in the tectonic regimes are attributed in part to changes in the magnitude of the boundary forces due to subduction processes. The overall perpendicular

  18. Unraveling an antique subduction process from metamorphic basement around Medellín city, Central Cordillera of Colombian Andes

    NASA Astrophysics Data System (ADS)

    Bustamante, Andres; Juliani, Caetano

    2011-10-01

    varies between 400 and 555 °C at pressures of 5-6 kbar in the retrograde metamorphic path. The El Retiro rocks evidence strong decompression with narrow variation in temperature, showing pressure values between 8.7 and 2.7 kbar at temperatures of 740-633 °C. These metamorphic fragments of the basement in the Central Cordillera of the Colombian Andes could represent a close relationship with an antique subduction zone.

  19. The Under-side of the Andes: Using Receiver Functions to Map the North Central Andean Subsurface

    NASA Astrophysics Data System (ADS)

    Ryan, J. C.; Beck, S. L.; Zandt, G.; Wagner, L. S.; Minaya, E.; Tavera, H.

    2012-12-01

    The Central Andean Uplift and Geodynamics of High Topography (CAUGHT) project is an interdisciplinary project to investigate connections between lithospheric removal, crustal shortening and surface uplift in the northern Bolivia and southern Peru region of the South American Andean orogen. The central Andes are defined by six major tectonomorphic provinces; the forearc, the volcanically active Western Cordillera (WC, ~6 km elevation), the internally drained Altiplano (~4 km elevation), an inactive fold and thrust belt in the Eastern Cordillera (EC, ~6 km elevation), a lower elevation active fold and thrust belt in the Subandean (SA) zone and the Beni, a foreland basin. Forty seismic stations installed for the CAUGHT project were deployed between 13° and 18° S latitude, covering the transition zone where the Altiplano region pinches out in southern Peru, in an effort to better constrain the changing character of the crust and mantle lithosphere. Geologic studies across the northern Bolivian portion of the eastern Andean margin (15-17° S) have documented a total of 275 km of upper crustal shortening (McQuarrie et al, Tectonics, v27, 2008), which may be associated with crustal thickening and/or the removal of lithospheric material as a thickened lithosphere root becomes unstable. For this receiver function (converted wave) study, we have little coverage in the forearc and foreland, ~75 km spacing in most of the array, and a relatively dense ~20 km spaced profile along the Charaña-La Paz-Yucumo transect, the eastern portion of which is nearly coincident with the balanced cross-section of McQuarrie et al. (2008). Using the first year of available data, more than 1200 receiver functions have been calculated using an iterative deconvolution method, and stacked using the common conversion point (CCP) method, along profiles parallel to and nearly coincident to those used for the geologic shortening estimates. We identified arrivals for the Moho and generated a 3D map of

  20. Recent temperature trends in the South Central Andes reconstructed from sedimentary chrysophyte stomatocysts in Laguna Escondida (1742 m a.s.l., 38°28 S, Chile)

    NASA Astrophysics Data System (ADS)

    De Jong, R.; Schneider, T.; Hernández-Almeida, I.; Grosjean, M.

    2016-02-01

    In this study we present a quantitative, high resolution reconstruction of past austral winter length in the Chilean Andes at 38°S from AD 1920 to 2009. For Laguna Escondida, a nearly pristine lake situated on the flanks of the Andes at 1740 m above sea level, past variability in the duration of the winter season (Days T4 °C) was reconstructed. Because high elevation meteorological stations are absent in this region, the reconstruction provides novel insights into recent temperature trends in the central-southern Andes. As a cold-season temperature proxy, we used chrysophyte stomatocysts. This novel proxy for cold season temperature was so far applied successfully in the European Alps and Pyrenees but has not yet been tested in the Southern Hemisphere. The reconstruction in this study was based on a newly developed Transfer Function to estimate Days T4 °C (number of consecutive days with surface water temperatures at or below 4 °C) from sedimentary stomatocyst assemblages (R2boot = 0.8, RMSEPboot = 28.7 days (= half the standard deviation)). To develop a high quality TF model, sediment traps and thermistors were placed in thirty remote lakes along an altitude gradient (420-2040 m a.s.l.). Complete materials and data were collected in 24 lakes after one year. Detailed statistical analyses indicate that modern stomatocysts primarily respond to the length of the cold season. The TF model was then applied to the sedimentary stomatocysts from a 210Pb-dated short core of L. Escondida. Comparison to independent reanalysis data showed that reconstructed changes in Days T4°C provides detailed information on winter-spring temperature variability since AD 1920. The reconstruction shows that recent warming (onset in AD 1980) in the southern Chilean Andes was not exceptional in the context of the past century. This is in strong contrast to studies from the Northern Hemisphere. The finding is also in contrast to the cooling temperature trends which were detected using

  1. Reverse Faulting as a Crucial Mechanism for Magma Ascent in Compressional Volcanic Arcs: Field Examples from the Central Andes

    NASA Astrophysics Data System (ADS)

    Aron, F. A.; Gonzalez, G.; Cembrano, J. M.; Veloso, E. E.

    2010-12-01

    The nature of crustal deformation in active arcs and the feedback mechanisms between tectonics and magma transport constitute fundamental problems in the understanding of volcanic systems. Additionally, for geothermal energy exploration, a better understanding of how crustal architecture and stress field controls fluid ascent and heat transfer from deep levels to the surface is crucial. The Central Andes volcanic belt is an excellent, modern example of such systems but, the scarcity of good outcrops has limited our ability to define the relations between structure and volcanism. In the Salar de Atacama Basin of northern Chile, there are good exposures of folded and faulted Neogene units (continental sediments, volcanic rocks and ignimbrites) and reverse faults spatially and temporally related to volcanic edifices. The subsurface of the study area has been interpreted by previous authors as a thin-skinned, 6-8 km-deep, east-vergent compressional belt. We carried out structural mapping, Digital Elevation Models (DEMs) analyses, strain tensor analyses and fault-related fold kinematic modelling to assess the causal relationship between compressional deformation and magmatism in this region. Field observations indicate that the structures deformed progressively Oligocene-Miocene continental sedimentary units, the upper sedimentary infill of the Salar de Atacama basin (Pliocene-Present), and Pliocene-Pleistocene Ignimbrites. The topographic expression of the compressional belt corresponds to a set of subparallel, asymmetric, fault-related-folds, which can be seen in the field as prominent NS-trending ridges with heights ranging between 50 and 400 m. Furthermore, we found evidence of a ~100 km-long structure along the active magmatic arc, so-called Miscanti Fault. This fault represents the easternmost expression of the above mentioned compressional belt. Pleistocene-Holocene monogenetic cones and strato-volcanoes are located either at the hinge zone of fault

  2. Crustal deformation in the south-central Andes backarc terranes as viewed from regional broad-band seismic waveform modelling

    NASA Astrophysics Data System (ADS)

    Alvarado, Patricia; Beck, Susan; Zandt, George; Araujo, Mario; Triep, Enrique

    2005-11-01

    The convergence between the Nazca and South America tectonic plates generates a seismically active backarc region near 31°S. Earthquake locations define the subhorizontal subducted oceanic Nazca plate at depths of 90-120 km. Another seismic region is located within the continental upper plate with events at depths <35 km. This seismicity is related to the Precordillera and Sierras Pampeanas and is responsible for the large earthquakes that have caused major human and economic losses in Argentina. South of 33°S, the intense shallow continental seismicity is more restricted to the main cordillera over a region where the subducted Nazca plate starts to incline more steeply, and there is an active volcanic arc. We operated a portable broad-band seismic network as part of the Chile-Argentina Geophysical Experiment (CHARGE) from 2000 December to 2002 May. We have studied crustal earthquakes that occurred in the back arc and under the main cordillera in the south-central Andes (29°S-36°S) recorded by the CHARGE network. We obtained the focal mechanisms and source depths for 27 (3.5 < Mw < 5.3) crustal earthquakes using a moment tensor inversion method. Our results indicate mainly reverse focal mechanism solutions in the region during the CHARGE recording period. 88 per cent of the earthquakes are located north of 33°S and at middle-to-lower crustal depths. The region around San Juan, located in the western Sierras Pampeanas, over the flat-slab segment is dominated by reverse and thrust fault-plane solutions located at an average source depth of 20 km. One moderate-sized earthquake (event 02-117) is very likely related to the northern part of the Precordillera and the Sierras Pampeanas terrane boundary. Another event located near Mendoza at a greater depth (~26 km) (event 02-005) could also be associated with the same ancient suture. We found strike-slip focal mechanisms in the eastern Sierras Pampeanas and under the main cordillera with shallower focal depths of ~5

  3. Migrating Ignimbrite Flares in the Central Andes, Implications for Crustal Evolution Based on Chemical, Isotopic, Geochronological, and GIS-Based Volumetric Data

    NASA Astrophysics Data System (ADS)

    Worner, G.; Brandmeier, M.; Freymuth, H.; Heistek, R. M.

    2014-12-01

    Temporal and compositional patterns of Neogene ignimbrites in the Central Andes were analysed using GIS and geostatistical modelling based on 203 digitized ignimbrite sheets for which geochronological, geochemical, and Sr-Nd-Pb-isotopic data on pumices as well as Sr-O isotopes on minerals from selected samples were compiled and compared to compositional and isotopic data from andesite lavas. Composition, timing, volumes and sources of erupted ignimbrite deposits are thus constrained and magma volumes through space and time are calculated. The total erupted ignimbrite magma volume of 31,000 km3 (minimum value) in the past 30 Ma indicate an average magmatic addition of 20-30 km3*Ma/km, similar to the basaltic "base"-flux for arc magmatism. Ignimbrite flare-ups are, however, rather punctuated, short-lived events well separated in space and time. There is a clear N-S "younging" of ignimbrite pulses from N to S at 19-24 Ma, 13-14 Ma, 6-10 Ma and 3-6 Ma. Ignimbrite eruptions occurred in the wake of subduction of the Juan-Fernandez ridge on the Nazca Plate passing below the Central Andes from N to S. Low angle subduction caused compression and fluid release is followed by massive inflow and melting of asthenospheric mantle when the slab steepened again after the passing of the ridge. This in turn caused massive melting within the crust aided by advective heat transport. Differences in chemical and isotopic composition of the large-volume ignimbrites are related to changes in crustal thickness, and different "preconditioning" during the Andean orogeny at a given space in time. Isotope data and whole rock compositional data suggest a higher degree of crustal assimilation for the younger Altiplano ignimbrites in the S (c. 50%) compared to the older (22-19 Ma) ignimbrites in the N were the crustal component is significantly less (20%). REE compositions reflect changes in crustal thickness with a "transition" at c. 13-9 Ma that can be related to accelerated crustal shortening

  4. Studies in Neotropical Paleobotany. XV. A Mio-Pliocene palynoflora from the Eastern Cordillera, Bolivia: implications for the uplift history of the Central Andes.

    PubMed

    Graham, A; Gregory-Wodzicki, K M; Wright, K L

    2001-09-01

    An assemblage of 33 fossil pollen and spores, recovered from the 3600-m high Pislepampa locality of E. W. Berry, Eastern Cordillera, Bolivia, adds considerably to our knowledge of three aspects of the region in late Neogene time: (1) the paleovegetation, (2) the paleoclimate, and (3) the paleoelevation of the Central Andes. The plant microfossils recognized are Isoetes, Lycopodium (three types), Cnemidaria, Cyathea (three types), Grammitis, Hymenophyllum, Pteris, trilete fern spores (two types), Danaea, monolete fern spores (four types), Podocarpus, Gramineae, Palmae, Ilex, cf. Oreopanax, Cavanillesia, cf. Pereskia, Compositae (three types), Ericaceae, Tetrorchidium, and unknowns (three types). The diversity of the Compositae suggest that this flora has a maximum age around the Miocene-Pliocene boundary, that is, 6-7 million years. All members of the paleocommunity presently grow in the bosque montano húmedo (cloud forest) along the eastern slope of the Central Andes of Bolivia, which occurs between MATs (mean annual temperatures) of ∼10° and 20°C. The Pislepampa flora probably represents the lower limits of this forest because the fossil leaves collected by Berry from the same locality all have entire margins, suggesting that the flora grew near the cloud forest-tropical forest transition. Presently, the lower limit of the cloud forest forest has MATs of ∼20°C, a mean annual precipitation between 1000 and 1500 mm, and that part containing most of the identified genera of fossil pollen is found at elevations ∼1200-1400 m. These conditions are thus inferred for the Pislepampa flora; however, because of the uncertainty of the magnitude of global climate change and of possible changes in the ecological range of plant genera, we estimate an error of at least ±1000 m for the paleoelevation estimate. When the total uplift is corrected for probable amounts of erosionally driven isostatic rebound, the paleoelevation estimate suggests that from one-third to one

  5. Evidence for Cenozoic extensional basin development and tectonic inversion south of the flat-slab segment, southern Central Andes, Chile (33° 36°S.L.)

    NASA Astrophysics Data System (ADS)

    Charrier, R.; Baeza, O.; Elgueta, S.; Flynn, J. J.; Gans, P.; Kay, S. M.; Muñoz, N.; Wyss, A. R.; Zurita, E.

    2002-04-01

    The mainly volcanic Cenozoic deposits that make up much of the western part of the Principal Cordillera in Central Chile are generally subdivided into two major units: an older Abanico or Coya-Machalı´ Formation and a younger Farellones Formation. Difficulty in differentiating these units has led to considerable debate. On the basis of the wide distribution, great thickness, and presence of sedimentary intercalations, it has been postulated that these arc volcanics were deposited in an intermontane basin; more recently, it has been proposed that this basin developed under extensional conditions and underwent subsequent tectonic inversion. We present field, geochronologic, geochemical, and thermal maturity data that support the latter interpretation. Collectively, this new information clarifies the stratigraphic, tectonic, and paleogeographic evolution of these deposits. The vast geographic extent of the Abanico Formation and lateral equivalents, which reach from at least 32°30' to 44°S along the Principal Cordillera, its great thickness, and the presence of repeated thick fluvial and lacustrine intercalations all indicate deposition in a large, strongly subsident, and probably north-south oriented basin, developed between middle to late Eocene and Oligocene. The unconformable contact with underlying Mesozoic units observed at several localities indicates that deposition followed a substantial erosional episode during late Cretaceous and/or early Cenozoic time. Basal deposits of the Abanico Formation near Termas del Flaco increase rapidly in thickness to the west. Still further to the west, a thick Abanico section contains, in its upper part, mammal fossils older than those found in the basal deposits near Termas. This evidence indicates a major space of deposition west of this locality, which had been filled before deposition took place at Termas. The east-vergent, high-angle El Fierro thrust fault on the east side of the westward-growing deposits is

  6. Late Quaternary Glaciations in the Central Peruvian Andes (10°-11°S) and Evidence for a Link to Heinrich Events

    NASA Astrophysics Data System (ADS)

    Smith, J. A.; Farber, D. L.; Finkel, R. C.; Rodbell, D. T.; Seltzer, G. O.

    2009-05-01

    Seven cosmogenic 10Be ages from a moraine in the Santuario Nacional Bosque de Piedras de Huayllay (BP) in the Western Cordillera of the central Peruvian Andes (10°59'S, 76°20'W, 4180-4200 masl) are consistent with 10Be ages on moraines in both the Eastern Cordillera (40-45 km to the east) and Nevado Jeulla Rajo (NJR) massif (10°00'S, 77°16'W) at the southern end of the Cordillera Blanca (150 km to the northwest). In the BP, 10Be ages are ~14-15 ka on four ignimbrite boulders, ~26 and ~20 ka on two quartz boulders, and ~45 ka on ignimbrite bedrock below the trimline in the valley wall. In the Eastern Cordillera bordering Lake Junin, the most extensive glaciations are >150 ka, but end moraines farther upvalley date to the local last glacial maximum (LLGM; 25-30 ka) and a late-glacial stillstand or readvance (14-18 ka). In NJR, 10Be ages indicate that the largest lateral moraines were deposited during similar intervals (27-32 ka and 14-18 ka). Avulsion of a glacial valley preserved an older, smaller pair of lateral moraines (56-65 ka) in NJR; correlative moraines were apparently not preserved in the Junin valleys. We have found no moraines in NJR that date to the global LGM (ca. 19-24 ka), but see some evidence for an advance ca. 40-48 ka. Outwash deposits (ca. 43-50 ka) located beyond the termini of NJR moraines are underlain by lodgement till that extends ca. 6 km across the Conococha Plain, suggesting that at least one older glaciation was far more extensive than any of the late Quaternary NJR advances dated by 10Be (ages calculated using CRONUS-Earth Online Calculator v. 2.2, Lal/Stone time-dependent scaling, and zero erosion). The timing of glacial advances in the central Peruvian Andes since 70 ka suggests a correlation to Heinrich events and associated southward shifts of the Intertropical Convergence Zone (ITCZ) in the Atlantic Ocean. We propose that Peruvian glaciers typically expanded when southward migration of the ITCZ resulted in increased

  7. Evaluation of TRMM Multi-satellite Precipitation Analysis (TMPA) performance in the Central Andes region and its dependency on spatial and temporal resolution

    NASA Astrophysics Data System (ADS)

    Scheel, M. L. M.; Rohrer, M.; Huggel, Ch.; Santos Villar, D.; Silvestre, E.; Huffman, G. J.

    2011-08-01

    Climate time series are of major importance for base line studies for climate change impact and adaptation projects. However, for instance, in mountain regions and in developing countries there exist significant gaps in ground based climate records in space and time. Specifically, in the Peruvian Andes spatially and temporally coherent precipitation information is a prerequisite for ongoing climate change adaptation projects in the fields of water resources, disasters and food security. The present work aims at evaluating the ability of Tropical Rainfall Measurement Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) to estimate precipitation rates at daily 0.25° × 0.25° scale in the Central Andes and the dependency of the estimate performance on changing spatial and temporal resolution. Comparison of the TMPA product with gauge measurements in the regions of Cuzco, Peru and La Paz, Bolivia were carried out and analysed statistically. Large biases are identified in both investigation areas in the estimation of daily precipitation amounts. The occurrence of strong precipitation events was well assessed, but their intensities were underestimated. TMPA estimates for La Paz show high false alarm ratio. The dependency of the TMPA estimate quality with changing resolution was analysed by comparisons of 1-, 7-, 15- and 30-day sums for Cuzco, Peru. The correlation of TMPA estimates with ground data increases strongly and almost linearly with temporal aggregation. The spatial aggregation to 0.5°, 0.75° and 1° grid box averaged precipitation and its comparison to gauge data of the same areas revealed no significant change in correlation coefficients and estimate performance. In order to profit from the TMPA combination product on a daily basis, a procedure to blend it with daily precipitation gauge measurements is proposed. Different sources of errors and uncertainties introduced by the sensors, sensor-specific algorithm aspects and the TMPA processing scheme

  8. Evaluation of TRMM Multi-satellite Precipitation Analysis (TMPA) performance in the Central Andes region and its dependency on spatial and temporal resolution

    NASA Astrophysics Data System (ADS)

    Scheel, M. L. M.; Rohrer, M.; Huggel, C.; Santos Villar, D.; Silvestre, E.; Huffman, G. J.

    2010-10-01

    Climate time series are of major importance for base line studies for climate change impact and adaptation projects. However, in mountain regions and in developing countries there exist significant gaps in ground based climate records in space and time. Specifically, in the Peruvian Andes spatially and temporally coherent precipitation information is a prerequisite for ongoing climate change adaptation projects in the fields of water resources, disasters and food security. The present work aims at evaluating the ability of Tropical Rainfall Measurement Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) to estimate precipitation rates at daily 0.25° × 0.25° scale in the Central Andes and the dependency of the estimate performance on changing spatial and temporal resolution. Comparison of the TMPA product with gauge measurements in the regions of Cuzco, Peru and La Paz, Bolivia were carried out and analysed statistically. Large biases are identified in both investigation areas in the estimation of daily precipitation amounts. The occurrence of strong precipitation events was well assessed, but their intensities were underestimated. TMPA estimates for La Paz show high false alarm ratio. The dependency of the TMPA estimate quality with changing resolution was analysed by comparisons of 1-, 7-, 15- and 30-day sums for Cuzco, Peru. The correlation of TMPA estimates with ground data increases strongly and almost linearly with temporal aggregation. The spatial aggregation to 0.5°, 0.75° and 1° grid box averaged precipitation and its comparison to gauge data of the same areas revealed no significant change in correlation coefficients and estimate performance. In order to profit from the TMPA combination product on a daily basis, a procedure to blend it with daily precipitation gauge measurements is proposed. Different sources of errors and uncertainties introduced by the sensors, sensor-specific algorithm aspects and the TMPA processing scheme are discussed

  9. Topaz magmatic crystallization in rhyolites of the Central Andes (Chivinar volcanic complex, NW Argentina): Constraints from texture, mineralogy and rock chemistry

    NASA Astrophysics Data System (ADS)

    Gioncada, Anna; Orlandi, Paolo; Vezzoli, Luigina; Omarini, Ricardo H.; Mazzuoli, Roberto; Lopez-Azarevich, Vanina; Sureda, Ricardo; Azarevich, Miguel; Acocella, Valerio; Ruch, Joel

    2014-01-01

    Topaz-bearing rhyolite lavas were erupted as domes and cryptodomes during the early history of the Late Miocene Chivinar volcano, in Central Andes. These are the only topaz rhyolite lavas recognized in Central Andes. Textural, mineralogical and geochemical data on the Chivinar rhyolites suggest that topaz crystallized from strongly residual, fluorine-rich, peraluminous silicate melts of topazite composition before the complete solidification of the lava domes. Crystallization of the rhyolitic magma began with sodic plagioclase and alkali feldspar phenocrysts in the magma chamber, followed by groundmass quartz + alkali feldspar + minor sodic plagioclase during dome emplacement, and terminated with quartz + topaz + vapour bubbles forming small scattered miaroles. Fluorine partitioning into the fluid phase occurred only in the final stage of groundmass crystallization. The magmatic origin of topaz indicates the presence of a fluorine-rich highly differentiated magma in the early history of the Chivinar volcano and suggests the possibility of rare metals mineralizations related to the cooling and solidification of a silicic magma chamber. A late fluid circulation phase, pre-dating the andesitic phase of the Chivinar volcano, affected part of the topaz rhyolite lavas. The presence of Nb, Ta and Mn minerals as primary accessories in the rhyolites and as secondary minerals in veins suggests a connection of the fluid circulation phase with the silicic magmatic system. Although at the edge of the active volcanic arc, the Chivinar topaz rhyolites are in correspondence of the transtensive Calama-Olacapato-El Toro fault system, suggesting preferred extensional conditions for the formation of magmatic topaz in convergent settings, consistently with evidence from other known cases worldwide.

  10. A new tectonic model for the development of the Eastern Cordillera, Altiplano, and Subandean zones, Bolivian Central Andes, 20[degrees]S latitude

    SciTech Connect

    Gubbels, T.L.; Isacks, B.L. ); Koch, R.W. )

    1993-02-01

    Construction of a regional transect across the central Andes at 20[degrees]S sheds new light on the relationship between the Altiplano, Eastern Cordillera (EC), and Subandean zones and allows us to refine the two-stage model of Isacks (1988) for the growth of the Central Andes. This new model is based on examination of the regional geology and geophysics, coupled with field investigations, satellite image analysis, and new Ar-Ar geochronology. In this model, widespread Oligocene to mid-Miocene compressional deformation in the Altiplano and EC was followed in the late-Miocene and Pliocene by thrusting localized east of the EC within the Subandean fold-thrust belt. During the first stage of deformation, the Altiplano basin underwent important subsidence and internal deformation. The EC was both deformed internally and thrust westwards over the Altiplano basin, while the present Subandean zone was the site of an early, broad foreland basin which received material eroded from the EC. During the second stage, beginning at [approximately]10 ma, deformation terminated within the EC and became concentrated within the fold-thrust belt in response to large scale overthrusting of the EC above the Brazilian shield; this resulted in major thrusting along the Cabalgamiento Frontal Principal (CFP), which soles into the master Subandean decollement, and [approximately]100 km of telescoping within the early, broad foreland basin. In the EC, this second stage is marked by the elaboration of a regionally extensive erosion surface, ponding of gravels in shallow basins, and the emplacement of giant ignimbrite sheets. The Eastern Cordillera can thus be thought of as a crustal-scale wedge which has been extruded upward and outward on alternate sides during successive stages of late Cenozoic deformation. This motion has served to drive subsidence in both the Altiplano and Subandean foreland basins, as well as shortening in the fold-thrust belt.

  11. Neotectonic reactivation of the western section of the Malargüe fold and thrust belt (Tromen volcanic plateau, Southern Central Andes)

    NASA Astrophysics Data System (ADS)

    Sagripanti, Lucía; Rojas Vera, Emilio A.; Gianni, Guido M.; Folguera, Andrés; Harvey, Jonathan E.; Farías, Marcelo; Ramos, Victor A.

    2015-03-01

    This study examines the neotectonic deformation and development of the Tromen massif, a Quaternary retroarc volcanic field located in the western section of the Malargüe fold and thrust belt in the Southern Central Andes. The linkages between neotectonic deformation in the intra-arc zone and the recent retroarc structures of the Tromen volcanic plateau are not clearly understood. These retroarc deformations affect the mid-section of the fold and thrust belt, leaving to the east a 200 km-wide deformed zone that can be considered inactive over the last 12-10 Ma. This out-of-sequence deformation west of the orogenic front area has not been previously addressed in detail. In this study, exhaustive mapping is used to describe and discriminate structures with a neotectonic component from those fossilized by Pleistocene strata. Two balanced cross-sections are constructed showing the distribution of the youngest deformations and their relation to pre-Miocene structures. An important means for evaluating this is the morphometric and morphological analyses that allowed identification of perturbations in the fluvial network associated with active structures. In a broader perspective, neotectonic activity in the fold and thrust belt is discussed and inferred to be caused by local mechanical weakening of the retroarc zone, due to injection of asthenospheric material evidenced by magnetotelluric surveys. Thus, deformation imposed by the oblique convergence between South American and Nazca plates, while to the south being limited to the Liquiñe-Ofqui fault system that runs through the arc zone, in the retroarc area is located at the site of magmatic emplacement, presumably in association with a thermally weakened-upper crust. This control exemplifies the relationship that exists between surficial processes, magmatic emplacement and upper asthenospheric dynamics in the Southern Central Andes.

  12. The origin of the Loncopué Trough in the retroarc of the Southern Central Andes from field, geophysical and geochemical data

    NASA Astrophysics Data System (ADS)

    Rojas Vera, E. A.; Sellés, D.; Folguera, A.; Gímenez, M.; Ruíz, F.; Orts, D.; Zamora Valcarce, G.; Martínez, P.; Bechis, F.; Ramos, V. A.

    2014-12-01

    This work analyzes through field, geophysical, geochemical and geochronological data, a particular setting of the Southern Andes in which an extensional system is flanking the mountain front. This setting is represented by the Loncopué Trough, whose origin is discussed for this part of the Andes. This work reconstructs 3-dimensionally the structure of this basin and its evolution through time, since Jurassic times as a series of isolated depocenters, to Late Cretaceous-Eocene times with the construction of a positive relief that subsequently was relaxed through two extensional stages during the late Oligocene-early Miocene and the Pliocene-Quaternary respectively. The last episode of extension is characterized by an initial stage with a series of caldera-collapses in the latest Pliocene-early Quaternary. This passed to a stage of development of a broad basaltic plateau in pre- and inter-glacial times, circumscribed with new radiometric data to the Pleistocene. Quaternary products in northern and central Loncopué Trough have chemical relations that are intermediate between the arc front and the southern Loncopué Trough volcanic rocks studied in previous works. Thus, retroarc eruptions would be part of an extended arc configuration that goes from typical arc series in the northern part of the trough to within-plate series in the south. Low elastic thicknesses computed from gravity data in this work correlate with the area of retroarc volcanic activity. Magnetic data have allowed determining the Curie isotherm, showing two areas of relatively abnormal heat flow, one along the Loncopué Trough itself and the other in the foreland zone. This scenario is discussed through three main hypotheses: an occurrence linked to a slab-steepening after a shallow subduction in the area; co-seismic crustal stretching linked to giant earthquakes in the subduction zone; and, finally slab-tearing associated with asthenospheric upwelling.

  13. Influence of Sea Surface Temperature Anomalies in the tropical Atlantic and the East-Central Pacific on Precipitation Variability in the Central Andes (13°S - 18°S)

    NASA Astrophysics Data System (ADS)

    Otto, Marco; Maussion, Fabien; Scherer, Dieter

    2013-04-01

    The Andean mountain range is a climatic barrier that blocks low-level tropospheric circulations. The resulting two contrasts of precipitation are most pronounced in its tropical part. The transition between both contrasts takes place in the high Andes along a transitional precipitation gradient. A few studies have shown that spatio-temporal precipitation patterns of the tropical Andes were related to the Sea Surface Temperature (SST) either of the Pacific or the Atlantic, but the magnitude and resulting spatial precipitation patterns are still in question. This study identifies spatio-temporal precipitation patterns that are highly correlated to time-delayed monthly SST-anomalies in both oceanic regions. The analysis was based on precipitation data from the Tropical Rainfall Measuring Mission (TRMM). Time series of monthly SST-anomalies were derived from the East-Central Tropical Pacific (Niño 3.4) and the Tropical Southern Atlantic (TSA). Precipitation data were filtered by applying wind direction filters at different tropospheric pressure levels derived from ERA-Interim. Highly significant (p<0.01) coefficients of determination up to 0.8 were found by multiple linear correlations using both data-sets of SST-anomalies as predictors for precipitation in austral summer (December to February: DJF). The strongest relationship was found in the semi-arid West Cordillera of the Andes within the study region. Here, a time-lag of one month in Pacific SST-anomalies reviled forecast potential for precipitation in DJF. A 61-year time series of DJF precipitation was computed based on the derived regression function. The results indicated a negative trend in computed DJF precipitation of - 1.2 mm per year due to a significant positive trend of January SST-anomalies in the Tropical South Atlantic.

  14. New Elemental and Isotopic Data From Mafic Lavas on the Puna Plateau and Re-Examining the Geochemical Signature of Convective Lithospheric Removal in the Central Andes

    NASA Astrophysics Data System (ADS)

    Murray, K. E.; Ducea, M. N.; Reiners, P. W.

    2009-12-01

    Foundering or delamination of the lower lithosphere into the convecting mantle is required by mass balance in convergent orogens such as the central Andes. In the central Andean volcanic zone (CVZ), late Miocene to Recent mafic lavas erupted on the Puna plateau are small volume fissure flows and cinder cones classically cited as evidence of convective lithospheric removal, in concert with a suite of observations including high surface elevation (>4000m) and anomalously thin lithosphere relative to other parts of the CVZ. Mafic lavas provide the best available geochemical window into the recent history of the upper mantle in this and other regions. However, an increasing number of elemental and isotopic data suggest that these melts are less distinct from the neighboring arc magmatism than originally predicted. This observation weakens the hypothesis that there is a distinct geochemical fingerprint for so-called delamination magmatism, while advancing our understanding of the size of delaminating bodies and the timescales over which they detach from the lithosphere and interact with the mantle wedge. In this contribution, we present elemental and radiogenic isotopic data from 20 newly sampled mafic lavas from the Puna plateau (24.5°S to 27°S). Preliminary major element analyses show that the Puna lavas are high-K to shoshonitic in composition, in broad agreement with other mafic lavas sampled though out the region. Several sampled flows contain xenotliths of granitoid composition, which likely represent the crustal end member that contributed to the more evolved lavas. Along with major, trace and rare earth element analyses, we will present 87Sr/86Sr and 143Nd/144Nd data to further characterize source regions of these melts. In sum, these data will allow us to (1) expand the spatial coverage of this dataset in the central Andes, (2) contribute to the effort to parse contributions from the subcontinental lithosphere, asthenosphere, subduction-related fluids, and

  15. Fissural volcanism, polygenetic volcanic fields, and crustal thickness in the Payen Volcanic Complex on the central Andes foreland (Mendoza, Argentina)

    NASA Astrophysics Data System (ADS)

    Mazzarini, F.; Fornaciai, A.; Bistacchi, A.; Pasquarè, F. A.

    2008-09-01

    Shield volcanoes, caldera-bearing stratovolcanoes, and monogenetic cones compose the large fissural Payen Volcanic Complex, located in the Andes foreland between latitude 35°S and 38°S. The late Pliocene-Pleistocene and recent volcanic activity along E-W trending eruptive fissures produced basaltic lavas showing a within-plate geochemical signature. The spatial distribution of fractures and monogenetic vents is characterized by self-similar clustering with well defined power law distributions. Vents have average spacing of 1.27 km and fractal exponent D = 1.33 defined in the range 0.7-49.3 km. The fractal exponent of fractures is 1.62 in the range 1.5-48.1 km. The upper cutoffs of fractures and vent fractal distributions (about 48-49 km) scale to the crustal thickness in the area, as derived from geophysical data. This analysis determines fractured media (crust) thickness associated with basaltic retroarc eruptions. We propose that the Payen Volcanic Complex was and is still active under an E-W crustal shortening regime.

  16. Hydro-isostatic deflection and tectonic tilting in the central Andes: Initial results of a GPS survey of Lake Minchin shorelines

    NASA Technical Reports Server (NTRS)

    Bills, Bruce G.; De Silva, Shanaka L.; Currey, Donald R.; Emenger, Robert S.; Lillquist, Karl D.; Donnellan, Andrea; Worden, Bruce

    1994-01-01

    Sufficiently large lake loads provide a means of probing rheological stratification of the crust and upper mantle. Lake Minchin was the largest of the late Pleistocene pluvial lakes in the central Andes. Prominent shorelines, which formed during temporary still-stands in the climatically driven lake level history, preserve records of lateral variations in subsequent net vertical motions. At its maximum extent the lake was 140 m deep and spanned 400 km N-S and 200 km E-R. The load of surficial water contained in Lake Minchin was sufficient to depress the crust and underlying mantle by 20-40 m, depending on the subjacent rheology. Any other differential vertical motions will also be recorded as departures from horizontality of the shorelines. We recently conducted a survey of shoreline elevations of Lake Minchin with the express intent of monitoring the hydro-isostatic deflection and tectonic tilting. Using real-time differential Global Positioning System (GPS), we measured topographic profiles across suites of shorelines at 15 widely separated locations throughout the basin. Horizontal and vertical accuracies attained are roughly 30 and 70 cm, respectively. Geomorphic evidence suggests that the highest shoreline was occupied only briefly (probably less than 200 years) and radiocarbon dates on gastropod shells found in association with the shore deposits constrain the age to roughly 17 kyr. The basin-side pattern of elevations of the highest shoreline is composed of two distinct signals: (27 +/- 1) m of hydro-isostatic deflection due to the lake load, and a planar tilt with east and north components of (6.8 +/- 0.4) 10(exp -5) and 9-5.3 +/- 0.3) 10(exp -5). This rate of tilting is too high to be plausibly attributed to steady tectonism, and presumably reflects some unresolved combination of tectonism plus the effects of oceanic and lacustrine loads on a laterally heterogeneous substrate. The history of lake level fluctuations is still inadequately known to allow

  17. Modern rainfall amounts and water stable isotope data from the South Central Andes of NW Argentina: Impacts of orographic barriers and plateau topography

    NASA Astrophysics Data System (ADS)

    Rohrmann, A.; Strecker, M. R.; Bookhagen, B.; Sachse, D.; Mulch, A.

    2011-12-01

    The Andes constitute a major orographic barrier to atmospheric circulation systems on a hemispheric scale. Moisture-bearing air masses, drawn into a seasonal low-pressure system in the Chaco lowland to the east of the orogen, rise progressively along the eastern flanks of the orogen and cool adiabatically during their ascent, resulting in summer thunderstorms and heavy rainfall within the lowermost ~1.5 km elevation. Focused precipitation along the eastern flanks of the orogen and leeward aridification are characteristic of the entire length of the South Central Andes, and are manifested by an across-strike decrease in vegetation cover and fluvial transport efficiency. To assess the effectiveness of the present-day Andean orographic barrier and its effect on the characteristics of δ18O and δD of precipitation, we collected 160 water samples along four E-W transects from the lowlands to the central part of the plateau between 22 and 27° S. These transects cross several orographic barriers and the Puna Plateau, including intervening intermontane basins and spanning > 4km of basin relief. We combined satellite-derived rainfall data (TRMM) with digital elevation models to evaluate the effects of local orographic barriers on modern precipitation distribution and calculated δ18O and δD values of precipitation based on Rayleigh distillation models for individual catchments along each orographic barrier. We then statistically compared the model results with the measured stable isotope values to test how well the observed data are predicted by the Rayleigh fractionation model. Most measured stream, river and rain waters fall 10 per mil above the Global Meteoric Water Line, whereas five samples from lakes on the plateau have highly negative d-excess values of -20 to -57 per mil, indicative of strong evaporation. Our preliminary results suggest a change in moisture sources, seen in water samples collected on the plateau itself. The data set represents the most complete

  18. Late Miocene high and rapid surface uplift and its erosional response in the Andes of central Chile (33°-35°S)

    NASA Astrophysics Data System (ADS)

    FaríAs, Marcelo; Charrier, Reynaldo; Carretier, SéBastien; Martinod, Joseph; Fock, AndréS.; Campbell, David; CáCeres, JoaquíN.; Comte, Diana

    2008-02-01

    We address the question of the late Cenozoic geomorphological evolution of the central Chile Andes (33°-35°S), using uplift markers, river incision, previous and new ages of volcanic bodies, and new fission track ages. The uplift markers consist of relicts of high elevated peneplains that evidence >2 km of regional surface uplift lasting ˜2 Ma with variable amount along an E-W transect. The eastern Coastal Cordillera was uplifted 1.5-2.1 km at 33-34°S and <1 km at 35°S, the western Principal Cordillera was uplifted ˜2 km, and the central eastern Principal Cordillera was uplifted >2.5 at 33°45'S and ˜1.5 km at 34°30'S. Erosional response to uplift was characterized by the retreat of a sharp knickpoint with celerities between 10 and 40 mm a-1. Extrapolation using a stream power law shows that uplift began shortly before 4 Ma or at 10.5-4.6 Ma (7.6 Ma central age) depending on the morphostructural units involved. The first alternative implies simultaneous uplift of the continental margin. The second model (the most reliable one) implies that the uplift affected together the eastern Coastal Cordillera and the Principal Cordillera, while the rest of the western fore arc subsided. This regional uplift can be mostly balanced by crustal thickening resulting from coeval shortening related to the out-of-sequence thrusting event in the Principal Cordillera and the uplift of the Frontal Cordillera. Simultaneously, emplacement of the southern edge of the flat slab subduction zone might have partially contributed to this uplift event.

  19. Applications of satellite imagery and digital topography to the construction of a crustal-scale transect across the central Andes at 20[degrees]S latitude

    SciTech Connect

    Gubbels, T.L.; Isacks, B.L. ); Ellis, J.M. )

    1993-02-01

    The central Andean plateau is one of the Earth's most remote and poorly mapped regions. The plateau has an average elevation of 3.7 km, and extends from central Peru to at least 30[degrees]S latitude. The plateau and flanking Subandean foldthrust belt (FTB) reach their greatest width near 20[degrees]S, and at this latitude both the FTB and the basin within the plateau (Altiplano basin) are areas of active hydrocarbon exploration. We have used Landsat TM imagery, stereoscopic SPOT imagery, and digital topography to construct a crustal-scale transect across the central Andes in order to better understand Andean tectonics at this latitude. Beginning at the Peru-Chile trench and continuing to the east, the transect crosses the Coastal Cordillera, Longitudinal Valley, Active Magmatic Arc, Altiplano basin, Eastern Cordillera, Subandean fold-thrust belt, and Subandean foreland basin. A digital elevation model across the entire region illustrates that the magmatic arc, Altiplano basin, and Eastern cordillera all lie within the plateau region. Satellite imagery across the transect illustrates the characteristic geology, structure, and geomorphology of each of the major morphotectonic regions, as well as the nature of their boundaries. The transect has led us to a number of new insights on Andean tectonics at this latitude. Most importantly, it supports a two-stage model of Andean Cenozoic growth in which a widespread Oligocene to mid-Miocene compressional deformation in the Altiplano and Eastern Cordillera is followed in the late Miocene and Pliocene by thrusting localized east of the Eastern Cordillera, forming the Subandean fold-thrust belt.

  20. Surnames and genetic structure of a high-altitude Quechua community from the Ichu River Valley, Peruvian Central Andes, 1825-1914.

    PubMed

    Pettener, D; Pastor, S; Tarazona-Santos, E

    1998-10-01

    Changes in isolation, inbreeding, population subdivision, and isonymous relationships are examined in six Quechua communities from the upper valley of the Ichu River in the Peruvian Central Andes (3700 m). All marriages registered between 1825 and 1914 in the Parish of Santa Ana were analyzed. The data (1680 marriages) were divided into 2 periods (1825-1870 and 1871-1914) and into the 6 villages that constitute the parish. Endogamy rates are between 81% and 100%, indicating high levels of reproductive isolation. The inbreeding indicated by isonymy (Ft, Fr, and Fn) is lower than in other mountain populations studied. Isonymy values, calculated from the different surname combinations made possible by the Ibero-American Surnames System, indicate a strong rejection of consanguineous marriages, particularly between patrilineal relatives, in agreement with the parental structure typical of Andean populations. The comparison between observed and expected repeated-pair values reveals a moderate level of subdivision within populations, which could be related to cultural and socioeconomic factors. Nonmetric multidimensional scaling was used to investigate temporal changes in the isonymous relationships among the communities. The results reveal a decrease in the interpopulational variability measured by surnames, in agreement with an increase in exogamy. Surnames and data contained in historical and demographic records yield reliable information, and they can be used to reconstruct the biological history of Amerindian populations over the last few centuries.

  1. Tectonic inversion and magmatism in the Lautaro Basin, northern Chile, Central Andes: A comparative approach from field data and analog models

    NASA Astrophysics Data System (ADS)

    Martínez, Fernando; Bonini, Marco; Montanari, Domenico; Corti, Giacomo

    2016-03-01

    We present the results of a series of analog models addressing the relationships between tectonic inversion and magmatism, taking the Lautaro Basin in northern Chile (27-28° S), Central Andes as a natural case. The experiments consisted of extension and orthogonal shortening of sand-silicone models to reproduce the tectonic inversion of a previous extensional system synchronous with the emplacement of analog magma. We analyzed how the variation in the rate of magma intrusion, shortening, and syn-compressive sedimentation may affect the final configuration of an inverted system, and the results were compared with field observations. Our results showed that (i) folding of syn-rift deposits and increased steepness of the master faults accommodate the shortening of the extensional system, (ii) magmatic intrusions condition the final geometries (top view and cross-section) of inverted normal faults in the models and in the Lautaro Basin, (iii) magma tends to migrate preferentially along the inverted faults, and accumulates beneath the faults and in the core of the inversion anticlines, (iv) the syn-inversion magmatism may indicate the migration pathways, which favor major lubrication and slip on the structures during their reactivation.

  2. Improved 3D density modelling of the Central Andes from combining terrestrial datasets with satellite based datasets

    NASA Astrophysics Data System (ADS)

    Schaller, Theresa; Sobiesiak, Monika; Götze, Hans-Jürgen; Ebbing, Jörg

    2015-04-01

    As horizontal gravity gradients are proxies for large stresses, the uniquely high gravity gradients of the South American continental margin seem to be indicative for the frequently occurring large earthquakes at this plate boundary. It has been observed that these earthquakes can break repeatedly the same respective segment but can also combine to form M>9 earthquakes at the end of longer seismic cycles. A large seismic gap left behind by the 1877 M~9 earthquake existed in the northernmost part of Chile. This gap has partially been ruptured in the Mw 7.7 2007 Tocopilla earthquake and the Mw 8.2 2014 Pisagua earthquake. The nature of this seismological segmentation and the distribution of energy release in an earthquake is part of ongoing research. It can be assumed that both features are related to thickness variations of high density bodies located in the continental crust of the coastal area. These batholiths produce a clear maximum in the gravity signal. Those maxima also show a good spatial correlation with seismic asperity structures and seismological segment boundaries. Understanding of the tectonic situation can be improved through 3D forward density modelling of the gravity field. Problems arise in areas with less ground measurements. Especially in the high Andes severe gaps exist due to the inaccessibility of some regions. Also the transition zone between on and offshore date data displays significant problems, particularly since this is the area that is most interesting in terms of seismic hazard. We modelled the continental and oceanic crust and upper mantle using different gravity datasets. The first one includes terrestrial data measured at a station spacing of 5 km or less along all passable roads combined with satellite altimetry data offshore. The second data set is the newly released EIGEN-6C4 which combines the latest satellite data with ground measurements. The spherical harmonics maximum degree of EIGEN-6C4 is 2190 which corresponds to a

  3. Tectonic styles and crustal shortening of the Central Andes "Pampean" flat-slab segment in northern Chile (27-29°S)

    NASA Astrophysics Data System (ADS)

    Martínez, Fernando; Arriagada, César; Peña, Matías; Deckart, Katja; Charrier, Reynaldo

    2016-01-01

    The Andean orogenic belt, located in the Central Andes "Pampean flat-slab" segment in northern Chile (27-29°S), is composed of two major tectonic regions: the Coastal Cordillera and the Frontal Cordillera. To understand their internal tectonic styles, history of growth and the shortening absorbed by the upper crustal structure of this segment, we combined regional geological mapping data, new ages obtained from radiometric U-Pb dating, and a semibalanced and restored cross-section 225.18 km in length. The results as shown in the previous Mesozoic extensional fault systems, established in northern Chile by the Gondwana breakup, have played a fundamental role in the orogenic buildup. The central structure is characterized by an asymmetric basin (Upper Cretaceous-Paleocene) confined by a doubly vergent fault system composed of inverted faults related to the edges of the Mesozoic Chañarcillo and Lautaro Basins. The U-Pb geochronological data obtained from synorogenic volcano-sedimentary deposits and the angular unconformities recorded between the Cenozoic geological units have revealed that the compressive deformation in this segment started at around ~ 80 Ma by tectonic inversion in the eastern Coastal Cordillera and western Frontal Cordillera, however, the presence of Paleocene and Miocene synorogenic successions at the footwall of the basement reverse faults of the Frontal Cordillera suggests a migration of Andean deformation from the west to the east during the Paleocene-Miocene by propagation of ramps involving inherited basement highs. The pre-compression restoration makes it possible to estimate 40.94 km of minimum shortening, concentrated by inversion anticlines and fault-controlled basement highs across the Frontal Cordillera.

  4. The geological and structural evolution of the Cerro Tuzgle Quaternary stratovolcano in the back-arc region of the Central Andes, Argentina

    NASA Astrophysics Data System (ADS)

    Norini, G.; Cogliati, S.; Baez, W.; Arnosio, M.; Bustos, E.; Viramonte, J.; Groppelli, G.

    2014-09-01

    The aim of our paper is to contribute to a better knowledge of the volcanism in the back-arc region of the Central Andes and its relationships with the basement geology, the stress field and the tectonic evolution, by studying in detail the stratigraphy and the structure of the Quaternary Cerro Tuzgle stratovolcano in the Puna Plateau. Field mapping and remote sensing analysis reveal the stratigraphic architecture, the geological evolution and the volcanotectonic interactions in the Cerro Tuzgle area. For the first time in a volcano of the Puna Plateau, synthemic units bounded by unconformity surfaces have been defined, unrevealing the temporal and spatial relationships between constructive and destructive phases of the volcano history. Our study indicates that after the emplacement of a small ignimbrite deposit and of few scattered lava domes, the central Cerro Tuzgle volcano built up throughout three distinct phases of edifice construction. The first of these constructive phases ended with a previously unreported destructive event, consisting of ≈ 0.5 km3, catastrophic sector collapse of the volcanic edifice, whose stratigraphic position and main characteristics have been identified. The study suggests that the regional stress regime and the topography of the substrata are the main non-magmatic factors controlling the constructive and destructive phases of the volcano, including the directions of magmatic intrusions, faulting and gravitational sector failure of the volcano. The integration of synthemic stratigraphy and volcanotectonic analysis in the study of volcanic edifices showed to be an effective methodological approach for the understanding of the magmatic and tectonic evolution of the Puna Plateau.

  5. ASTER Andes

    NASA Technical Reports Server (NTRS)

    2000-01-01

    In this image of the Andes along the Chile-Bolivia border, the visible and infrared data have been computer enhanced to exaggerate the color differences of the different materials. The scene is dominated by the Pampa Luxsar lava complex, occupying the upper right two-thirds of the scene. Lava flows are distributed around remnants of large dissected cones, the largest of which is Cerro Luxsar. On the middle left edge of the image are the Olca and Parumastrato volcanoes, which appear in blue due to a lack of vegetation (colored red in this composite). This image covers an area 60 kilometers (37 miles) wide and 60 kilometers (37 miles) long in three bands of the reflected visible and infrared wavelength region. It was acquired on April 7, 2000.

    The image is located at 21 degrees south latitude, 68.3 degrees west longitude.

    Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of International Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. science team leader; Moshe Pniel of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The primary goal of the ASTER mission is to obtain high-resolution image data in 14 channels over the entire land surface, as well as black and white stereo images. With revisit time of between 4 and 16 days, ASTER will provide the capability for repeat coverage of changing areas on Earth's surface.

    The broad spectral coverage and high spectral resolution of ASTER will provide scientists in numerous disciplines with critical information for surface mapping and monitoring dynamic conditions and temporal change. Examples of applications include monitoring glacial

  6. The Structure of the Crust and Uppermost Mantle Beneath the Central Andes from Ambient Noise Tomography: Imaging the Neogene to Modern Batholith

    NASA Astrophysics Data System (ADS)

    Ward, K. M.; Zandt, G.; Beck, S. L.; Porter, R. C.; Wagner, L. S.; Minaya, E.; Tavera, H.

    2012-12-01

    The Central Andes of southern Peru, Bolivia, and northern Chile (between ~10°S and ~35°S) comprise the largest orogenic plateau in the world associated with abundant arc volcanism, the Central Andean Plateau (CAP). The goal of this continental-scale Ambient Noise Tomography (ANT) project is to incorporate broadband seismic data from ~20 seismic networks deployed incrementally in the Central and Southern Andes from May 1994 through March 2012, to image the vertically polarized shear-wave velocity (Vsv) structure of the CAP. First-order correlations with our shallow results (~5 km) and the morphotectonic provinces as well as subtler geological features indicate our results are robust. Our major results include mapping a pervasive mid-crustal low-velocity zone (<3.25 km/s) underneath the western portion of the CAP and a locally ultra-low-velocity anomaly (~2.0 km/s) beneath the Altiplano-Puna Volcanic Complex (APVC). The presence of a large and laterality extensive low-velocity zone suggests either a zone of partial melt ("mush") associated with batholith formation at depth, a thermally weakened crust capable of lateral flow, or the presence of aqueous fluids. Magnetotelluric studies that overlap our images do not resolve a high conductivity anomaly across our low-velocity zone as expected in the presence of aqueous fluids or large interconnected zones of partial melt. Therefore, we dismiss them as likely explanations for our imaged low-velocity body outside of the APVC location. Working under the hypothesis that voluminous ignimbrites are the surface expression of batholith formation at depth as exemplified by the APVC, we combine our results with the locations of known Neogene ignimbrite eruptive centers and negative isostatic residual gravity anomalies and suggest the 3.25 km/s shear-wave velocity contour at 15 km depth generally outlines the extent of a Neogene to modern batholith, with isolated pockets of partial melt where velocities dip below 3.0 km/s. A

  7. Petrology and mineralogy of the La Peña igneous complex, Mendoza, Argentina: An alkaline occurrence in the Miocene magmatism of the Southern Central Andes

    NASA Astrophysics Data System (ADS)

    Pagano, Diego Sebastián; Galliski, Miguel Ángel; Márquez-Zavalía, María Florencia; Colombo, Fernando

    2016-04-01

    The La Peña alkaline igneous complex (LPC) is located in the Precordillera (32°41‧34″ S - 68°59‧48″ W) of Mendoza province, Argentina, above the southern boundary of the present-day flat-slab segment. It is a 19 km2 and 5 km diameter subcircular massif emplaced during the Miocene (19 Ma) in the Silurian-Devonian Villavicencio Fm. The LPC is composed of several plutonic and subvolcanic intrusions represented by: a cumulate of clinopyroxenite intruded by mafic dikes and pegmatitic gabbroic dikes, isolated bodies of malignite, a central intrusive syenite that develops a wide magmatic breccia in the contact with clinopyroxenite, syenitic and trachytic porphyries, a system of radial and ring dikes of different compositions (trachyte, syenite, phonolite, alkaline lamprophyre, tephrite), and late mafic breccias. The main minerals that form the LPC, ordered according to their abundance, are: pyroxene (diopside, hedenbergite), calcium amphibole (pargasite, ferro-pargasite, potassic-ferro-pargasite, potassic-hastingsite, magnesio-hastingsite, hastingsite, potassic-ferro-ferri-sadanagaite), trioctahedral micas (annite-phlogopite series), plagioclase (bytownite to oligoclase), K-feldspar (sanidine and orthoclase), nepheline, sodalite, apatite group minerals (fluorapatite, hydroxylapatite), andradite, titanite, magnetite, spinel, ilmenite, and several Cu-Fe sulfides. Late hydrothermal minerals are represented by zeolites (scolecite, thomsonite-Ca), epidote, calcite and chlorite. The trace element patterns, coupled with published data on Sr-Nd-Pb isotopes, suggest that the primary magma of the LPC was generated in an initially depleted but later enriched lithospheric mantle formed mainly by a metasomatized spinel lherzolite, and that this magmatism has a subduction-related signature. The trace elements pattern of these alkaline rocks is similar to other Miocene calc-alkaline occurrences from the magmatic arc of the Southern Central Andes. Mineral and whole

  8. Combining numerical modeling and stable isotope values to quantify groundwater recharge from the Chilean Andes to the Pampa del Tamarugal Basin, Atacama Desert, northern Chile

    NASA Astrophysics Data System (ADS)

    Dodd, J. P.; Pollyea, R.

    2014-12-01

    The Atacama Desert of northern Chile is one of the driest regions on Earth and receives less than 5mm of precipitation annually. The Pampa del Tamarugal (PdT) Basin contains the largest aquifer system in the region, yet the mechanisms and timing of aquifer recharge and continental-scale groundwater flux are poorly understood. Although there is little debate that the source of groundwater recharge is the higher elevation regions of the Andean Altiplano to the east of the PdT Basin, there remains much uncertainty surrounding the mechanisms and timing of aquifer recharge and continental-scale groundwater flux. Most recharge models of the PdT focus on surface water runoff and alluvial fan recharge on shorter time scales, but many of these models explicitly neglect deep flow pathways. Previous investigators have combined the thermal aquifer profile and 14C groundwater ages to propose an alternative conceptual model in which cold meteoric water infiltrates deep into the Cordillera before circulating upward into the PdT by thermal convection through fault-controlled migration pathways. Although this conceptual model provides a convincing theoretical argument for deep fluid circulation, it cannot constrain the magnitude of this deep recharge flux. In this work, we revisit deep-flow conceptual model by combining the spatial distribution of hydrogen and oxygen isotope values as groundwater tracers with a non-isothermal model of continental scale groundwater flow through a two-dimensional transect from the Chilean Andes to the PdT Basin. This work provides first-order estimates on the contribution of deep groundwater circulation within the PdT Aquifer, while providing a framework for (1) quantifying boundary conditions for high resolution models of groundwater resources within the PdT Aquifer, (2) assessing the influence of variable future climate scenarios for groundwater availability in the region, and (3) further integrating conservative tracers and numerical models for

  9. Spatial-temporal evolution of topography of the central Andes and implications for deep tectonic processes (Invited)

    NASA Astrophysics Data System (ADS)

    Garzione, C. N.; Auerbach, D. J.; Bershaw, J. T.; Kar, N.; Smith, J. J.

    2013-12-01

    Resolving the spatial and temporal evolution of changes in the elevation of mountain belts provides constraints on the geodynamic mechanisms that caused surface uplift of these regions. Several recent studies in the Central Andean plateau (between 13°S and 28°S) have used multiple climate proxies to demonstrate punctuated (several myr) changes in the composition of meteoric water and surface temperature inferred to reflect significant (≥1000 m) surface uplift. These studies suggest that different regions experienced surface uplift at different times. In comparison with crustal thickening histories derived from reconstructions of crustal shortening, it is also clear that crustal thickening and surface uplift are temporally decoupled, with significant crustal thickening preceding punctuated surface uplift events by several tens of millions of years. Here we compile results from paleoclimate studies of the Central Andean plateau to infer regional patterns of surface uplift. Limited paleoclimate data and geologic evidence indicate that the Eastern Cordillera experienced an earlier pulse of surface uplift than the Altiplano zone, associated with an eastward sweep of magmatism that marks the current limits of the plateau. Within the Altiplano zone, the southern Altiplano appears to have risen beginning in middle Miocene time and continuing through late Miocene time. During this time, the north-central Altiplano remained low and experienced increasing rates of sedimentation. In late Miocene time, sedimentation rates slowed dramatically at the same time that climate proxy data suggest rapid surface uplift of the north-central Altiplano. The northernmost Altiplano of Peru experienced a pulse of surface uplift in middle Miocene to early Pliocene time, with the exact timing unconstrained as of yet. Crustal shortening reconstructions from the southern through the north-central plateau (between 17°S and 24°S) yield upper estimates that range between 300×20 km, sufficient

  10. Space-time variations of stresses in the Miocene-Quaternary along the Calama-Olacapato-El Toro Fault Zone, Central Andes

    NASA Astrophysics Data System (ADS)

    Lanza, F.; Tibaldi, A.; Bonali, F. L.; Corazzato, C.

    2013-05-01

    We describe the temporal and spatial changes in the tectonic state of stress occurred during the Miocene-Quaternary in the trans-orogen area of the Calama-Olacapato-El Toro (COT) fault zone in the Central Andes, at about 24°S within the northern portion of the Puna Plateau. This work sheds new light on the complexity of stress pattern distribution in general, and contributes to the analysis of the relationships between tectonics and volcanism, and of the seismic hazard of the area. Field geological surveys, along with kinematic analysis and numerical inversion of ~ 140 new fault-slip measurements, have revealed that this portion of the COT zone, previously considered a continuous, long-lived lineament, in reality has been subjected to three different kinematic regimes: 1) a Miocene transpressional phase with the maximum principal stress (σ1) chiefly trending NNE-SSW; 2) an extensional phase that started by 9 Ma, with a horizontal NW-SE-trending minimum principal stress (σ3), and 3) a left-lateral strike-slip phase with a horizontal ~ E-W σ1 and ~ N-S σ3 dating to the late Pliocene-Quaternary, which decreases toward the westernmost part of the studied zone, where it transitions to extension producing a N-S-trending graben structure. Hence, even if transcurrence is still active in the eastern portion of the COT, as focal mechanisms of crustal earthquakes indicate, our study demonstrates that extension is becoming the predominant structural style of deformation, at least in the western region. The major changes in the tectonic regimes are attributed to changes in the magnitude of the boundary forces due to subduction processes, whereas gravitational effect of a thickened crust might be responsible for the overall orogen-perpendicular extension.

  11. Sedimentary record of regional deformation and dynamics of the thick-skinned southern Puna Plateau, central Andes (26-27°S)

    NASA Astrophysics Data System (ADS)

    Zhou, Renjie; Schoenbohm, Lindsay M.; Sobel, Edward R.; Carrapa, Barbara; Davis, Donald W.

    2016-01-01

    The Puna Plateau, adjacent Eastern Cordillera and the Sierras Pampeanas of the central Andes are largely characterized by thick-skinned, basement-involved deformation. The Puna Plateau hosts ∼N-S trending bedrock ranges bounded by deep-seated reverse faults and sedimentary basins. We contribute to the understanding of thick-skinned dynamics in the Puna Plateau by constraining regional kinematics of the poorly understood southern Puna Plateau through a multidisciplinary approach. On the southeastern plateau, sandstone modal composition and detrital zircon U-Pb and apatite fission-track data from Cenozoic strata indicate basin accumulation during the late Eocene to early Oligocene (∼38-28 Ma). Provenance analysis reveals the existence of a regional-scale basin covering the southern Puna Plateau during late Eocene to early Oligocene time (∼38-28 Ma) that was sourced from both the western plateau and the eastern plateau margin and had a depocenter located to the west. Petrographic and detrital zircon U-Pb data reveal erosion of proximal western and eastern sources after ∼12 Ma, in mid-late Miocene time. This indicates that the regional basin was compartmentalized into small-scale depocenters by the growth of basement-cored ranges continuing into the late Miocene (∼12-8 Ma). We suggest that the Cenozoic history of the southern Puna Plateau records the formation of a regional basin that was possibly driven by lithospheric flexure during the late Eocene to early Oligocene, before the growth of distributed basement-cored ranges starting as early as the late Oligocene.

  12. Tectono-stratigraphic evolution of the Canete Basin, Lima, Peru, a plate tectonic model for the Mesozoic evolution of the Central Andes

    SciTech Connect

    Aleman, A.M. )

    1993-02-01

    An arc-trench system has been active in the Central Andes since at least since Late Triassic. This Mesozoic margin was characterized by subduction-erosion processes, PreMesozoic metamorphic outer basement high, pervasive extension, tectonic inversion, sporadic igneous activity and segmentation of the arc. Episodic variations in the tectonic evolution of the associated basins were controlled by the variable angle of subduction, age of the subducted plate, rate and angle of convergence, and the relative motion of the Farallon and South America Plates. The Canete Basin is an elongate frontal arc basin, subparallel to the arc, which documents the early evolution of the Andean Orogeny. In the Canete Basin, the oldest arc volcanism is documented by the interbedded tuffs, lava flows and tuffaceous marine shales of the Late Jurassic Puente Piedra Group which was deposited along a series of isolated and elongated troughs that formed adjacent to the arc. During Late Berriasian the arc subsided and the lithofacies changed from arc to continental derived lithologies. The shallow marine, quartz rich Morro Solar Group was derived from the uplifted metamorphic basement high in the west, as the result of ensialic extension. Locally, volcanic quiescence was interrupted by deposition of the volcaniclastic rich Pucusana Formation. The Late Hauterivian to Aptian Lima Group consists of lime mudstones, shales and subordinated gypsum and bioclastic limestones with volcaniclastic and lava flow facies of the Chilca Group. Stratigraphic relationship rapid changes in thickness and facies of this unit document the development of an incipient arc and the persistence of ensialic extension prior to the maximum paroxysm of volcanic activity of the overlying Albian to Cenomanian Chillon Group. Interbedded volcaniclastic sandstones, lava flows, hyaloclastic breccias and the tuffaceous shales of the Chillon Group were coeval with the early phases of emplacement of the Coastal Batholith (CB).

  13. Role of maca (Lepidium meyenii) consumption on serum interleukin-6 levels and health status in populations living in the Peruvian Central Andes over 4000 m of altitude.

    PubMed

    Gonzales, Gustavo F; Gasco, Manuel; Lozada-Requena, Ivan

    2013-12-01

    Lepidium meyenii (Maca) is a plant that grows at over 4,000 m above sea level in the central Peruvian Andes. The hypocotyls of this plant are traditionally consumed for their nutritional and medicinal properties. The aim of this study was to determine the health status based on a health related quality of life (HRQL) questionnaire (SF-20) and serum levels of interleukin 6 (IL-6) in subjects that are maca consumers. For this, a cross-sectional study was designed to be performed in 50 subjects from Junin (4,100 m): 27 subjects were maca consumers and 23 were non-consumers. The SF-20 survey is used to obtain a summary measure of health status. The stand up from a chair and sit down (SUCSD) test (to assess lower-extremity function), hemoglobin measurement, blood pressure, sexual hormone levels, serum IL-6 levels and the score of chronic mountain sickness (CMS) were evaluated. Testosterone/estradiol ratio (P <0.05), IL-6 (P < 0.05) and CMS score were lower, whereas the health status score was higher, in maca consumers when compared to non-consumers (P < 0.01). A greater proportion of maca consumers successfully completed the SUCSD test compared to non-consumers (P < 0.01), showing a significant association with lower values of serum IL-6 (P < 0.05). In conclusion, consumption of maca was associated with low serum IL-6 levels and in turn with better health status scores in the SF-20 survey and low chronic mountain sickness scores. PMID:23934543

  14. Geometry and kinematics of the Andean thick-skinned thrust systems: Insights from the Chilean Frontal Cordillera (28°-28.5°S), Central Andes

    NASA Astrophysics Data System (ADS)

    Martínez, F.; Arriagada, C.; Valdivia, R.; Deckart, K.; Peña, M.

    2015-12-01

    The structure of the Chilean Frontal Cordillera, located over the Central Andes flat-slab subduction segment (27°-28.5°S), is characterized by a thick-skinned deformation, affecting both the pre-rift basement and the Mesozoic and Cenozoic infill of the NNE-SSW Lautaro and Lagunillas Basins, which were developed during the Pangea-Gondwana break-up. The compressive deformation show a complex interaction between Mesozoic rift structures and thrust systems, affecting a suite of Permo-Triassic (258-245 Ma) granitic blocks. We used a combination of geological mapping, new structural data, balanced and restored cross sections and geochronological data to investigate the geometry and kinematics of the Andean thick-skinned thrust systems of the region. The thrust systems include double-vergent thick-skinned thrust faults, basement-cored anticlines and minor thin-skinned thrusts and folds. The presence of Triassic and Jurassic syn-rift successions along the hanging wall and footwall of the basement thrust faults are keys to suggest that the current structural framework of the region should be associated with the shortening of previous Mesozoic half grabens. Based on this interpretation, we propose a deformation mechanism characterized by the tectonic inversion of rift-related faults and the propagation of basement ramps that fold and cut both, the early normal faults and the basement highs. New U-Pb ages obtained from synorogenic deposits (Quebrada Seca and Doña Ana formations) indicate at least three important compressive pulses. A first pulse at ˜80 Ma (Late Cretaceous), a second pulse related to the K-T phase of Andean deformation and, finally, a third pulse that occurred during the lower Miocene.

  15. Role of maca (Lepidium meyenii) consumption on serum interleukin-6 levels and health status in populations living in the Peruvian central Andes over 4000 m of altitude

    PubMed Central

    Gonzales, Gustavo F.; Gasco, Manuel; Lozada, Ivan

    2013-01-01

    Lepidium meyenii (Maca) is a plant that grows at over 4000 meters above sea level in the central Peruvian Andes. The hypocotyls of this plant are traditionally consumed for their nutritional and medicinal properties. The aim of this study was to determine the health status based on a health related quality of life (HRQL) questionnaire (SF-20) and serum levels of interleukin 6 (IL-6) in subjects that are maca consumers. For this, a cross-sectional study was designed to be performed in 50 subjects from Junin (4100 m): 27 subjects were maca consumers and 23 were non-consumers. The SF-20 survey is used to obtain a summary measure of health status. The stand up from a chair and sit down (SUCSD) test (to assess lower-extremity function), hemoglobin measurement, blood pressure, sexual hormone levels, serum IL-6 levels and the score of chronic mountain sickness (CMS) were evaluated. Testosterone/estradiol ratio (P≪0.05), IL-6 (P<0.05) and CMS score were lower, whereas the health status score was higher, in maca consumers when compared to non-consumers (P<0.01). A greater proportion of maca consumers successfully completed the SUCSD test compared to non-consumers (P<0.01), showing a significant association with lower values of serum IL-6 (P<0.05). In conclusion, consumption of maca was associated with low serum IL-6 levels and in turn with better health status scores in the SF-20 survey and low chronic mountain sickness scores. PMID:23934543

  16. Role of maca (Lepidium meyenii) consumption on serum interleukin-6 levels and health status in populations living in the Peruvian Central Andes over 4000 m of altitude.

    PubMed

    Gonzales, Gustavo F; Gasco, Manuel; Lozada-Requena, Ivan

    2013-12-01

    Lepidium meyenii (Maca) is a plant that grows at over 4,000 m above sea level in the central Peruvian Andes. The hypocotyls of this plant are traditionally consumed for their nutritional and medicinal properties. The aim of this study was to determine the health status based on a health related quality of life (HRQL) questionnaire (SF-20) and serum levels of interleukin 6 (IL-6) in subjects that are maca consumers. For this, a cross-sectional study was designed to be performed in 50 subjects from Junin (4,100 m): 27 subjects were maca consumers and 23 were non-consumers. The SF-20 survey is used to obtain a summary measure of health status. The stand up from a chair and sit down (SUCSD) test (to assess lower-extremity function), hemoglobin measurement, blood pressure, sexual hormone levels, serum IL-6 levels and the score of chronic mountain sickness (CMS) were evaluated. Testosterone/estradiol ratio (P <0.05), IL-6 (P < 0.05) and CMS score were lower, whereas the health status score was higher, in maca consumers when compared to non-consumers (P < 0.01). A greater proportion of maca consumers successfully completed the SUCSD test compared to non-consumers (P < 0.01), showing a significant association with lower values of serum IL-6 (P < 0.05). In conclusion, consumption of maca was associated with low serum IL-6 levels and in turn with better health status scores in the SF-20 survey and low chronic mountain sickness scores.

  17. The Cerro Guacha Caldera complex: An Upper Miocene-Pliocene polycyclic volcano-tectonic structure in the Altiplano Puna Volcanic Complex of the Central Andes of Bolivia

    NASA Astrophysics Data System (ADS)

    Iriarte, R.; de Silva, S. L.; Jimenez, N.; Ort, M. H.

    2011-12-01

    Four multicyclic complex calderas and smaller ignimbrite shields located within the Altiplano Puna Volcanic Complex of the Central Andes erupted 13000 km3 of magma within the last 11 Ma. One of the largest and most complex of these is the 5.6 to 1 Ma Cerro Guacha Caldera complex in SW Lipez, Bolivia. Ar-Ar age determinations and paleomagnetic signatures suggest that the Cerro Guacha Caldera was formed by two major eruptions, caldera collapse, resurgence cycles and several smaller eruptions. Two major ignimbrites of super-eruption magnitude are found with 40Ar-39Ar from biotites and sanidines of 5.65±0.01Ma for the 1300 km3 (magma volume) Guacha ignimbrite and 3.49±0.01Ma for the 800 km3 Tara Ignimbrite. The last major eruption occurred on the western flank producing the 1.72±0.02 Ma Puripica Chico Ignimbrite with a volume of approximately 10 km3. Characteristic remanent magnetization data (ChRM) for these ignimbrites show that the Guacha has reverse polarity, while the Tara is normally polarized and the magnetic fingerprints have allowed their current full extents to be identified. The Guacha ignimbrite extends over 70 km north and south of the caldera and is distributed over an area of almost 5000 km2. The Tara ignimbrite covers an area of almost 4000 km2 and extends southwards almost 70 km, where it ponded in La Pacana caldera. A conspicuous lineament of volcanic structures towards the caldera's easternmost edge, along with a flat surface (moat), welded ignimbrites, and sedimentary lacustrine sequences suggest an earlier 60x40 km outer collapse associated with the Guacha explosive episode. A central graben consisting of Guacha welded ignimbrite is related to the first episode of resurgence. Evidence of a second 30x15 km inner collapse scarp includes offset of welded Guacha ignimbrites and alignment of lava domes equivalent in age to the Tara ignimbrite. A second resurgence episode is suggested by the presence of a central block consisting primarily of welded

  18. Meta-information system facilitates use of complex data related to Andes

    NASA Astrophysics Data System (ADS)

    Ott, N.; Götze, H.-J.; Schmidt, S.; Burger, H.; Alten, M.

    Studies of the Collaborative Research Center 267, "Deformation Processes in the Andes," focus on interdisciplinary geoscientific research in the central and Patagonian Andes involving all disciplines of geoscience. The combination of geophysical and geological field research, Global Positioning System monitoring, penological and geochemical analysis, age dating, and remote sensing provides new insight into the structure and tectonic evolution of the Andes.

  19. Arc-oblique fault systems: their role in the Cenozoic structural evolution and metallogenesis of the Andes of central Chile

    NASA Astrophysics Data System (ADS)

    Piquer, Jose; Berry, Ron F.; Scott, Robert J.; Cooke, David R.

    2016-08-01

    The evolution of the Main Cordillera of Central Chile is characterized by the formation and subsequent inversion of an intra-arc volcano-tectonic basin. The world's largest porphyry Cu-Mo deposits were emplaced during basin inversion. Statistically, the area is dominated by NE- and NW-striking faults, oblique to the N-striking inverted basin-margin faults and to the axis of Cenozoic magmatism. This structural pattern is interpreted to reflect the architecture of the pre-Andean basement. Stratigraphic correlations, syn-extensional deposits and kinematic criteria on fault surfaces show several arc-oblique structures were active as normal faults at different stages of basin evolution. The geometry of syn-tectonic hydrothermal mineral fibers, in turn, demonstrates that most of these structures were reactivated as strike-slip ± reverse faults during the middle Miocene - early Pliocene. Fault reactivation age is constrained by 40Ar/39Ar dating of hydrothermal minerals deposited during fault slip. The abundance and distribution of these minerals indicates fault-controlled hydrothermal fluid flow was widespread during basin inversion. Fault reactivation occurred under a transpressive regime with E- to ENE-directed shortening, and was concentrated around major plutons and hydrothermal centers. At the margins of the former intra-arc basin, deformation was largely accommodated by reverse faulting, whereas in its central part strike-slip faulting was predominant.

  20. Discrimination and supervised classification of volcanic flows of the Puna-Altiplano, Central Andes Mountains using Landsat TM data

    NASA Technical Reports Server (NTRS)

    Mcbride, J. H.; Fielding, E. J.; Isacks, B. L.

    1987-01-01

    Landsat Thematic Mapper (TM) images of portions of the Central Andean Puna-Altiplano volcanic belt have been tested for the feasibility of discriminating individual volcanic flows using supervised classifications. This technique distinguishes volcanic rock classes as well as individual phases (i.e., relative age groups) within each class. The spectral signature of a volcanic rock class appears to depend on original texture and composition and on the degree of erosion, weathering, and chemical alteration. Basalts and basaltic andesite stand out as a clearly distinguishable class. The age dependent degree of weathering of these generally dark volcanic rocks can be correlated with reflectance: older rocks have a higher reflectance. On the basis of this relationship, basaltaic lava flows can be separated into several subclasses. These individual subclasses would correspond to mappable geologic units on the ground at a reconnaissance scale. The supervised classification maps are therefore useful for establishing a general stratigraphic framework for later detailed surface mapping of volcanic sequences.

  1. Neogene to Quaternary ash deposits in the Coastal Cordillera in northern Chile: Distal ashes from supereruptions in the Central Andes

    NASA Astrophysics Data System (ADS)

    Breitkreuz, Christoph; de Silva, Shanaka L.; Wilke, Hans G.; Pfänder, Jörg A.; Renno, Axel D.

    2014-01-01

    Silicic volcanic ash deposits investigated at 14 localities between 22° and 25°S in the Chilean Coastal Cordillera are found to be the distal ash fall from supereruptions in the Central Andean cordillera several hundreds of kilometers to the east. Depositional textures, modal composition and granulometry of the ashes and tuffs (the latter lithified by halite and gypsum under ultra-arid conditions) allow for a distinction between primary fallout/aeolian deposits (mean 4-5 Φ, sorting 1.5-2 Φ) and secondary deposits that formed by down wash from hill slopes during local rain fall. Primary volcanic components comprise two types of glass shards (with small stretched vesicles and coarse-walled with rounded to elliptic vesicles), and biotite.

  2. Evidence of the Timing and Rate of Uplift of Central Peruvian Andes from Deuterium Isotopes in Volcanic Glass

    NASA Astrophysics Data System (ADS)

    Winton, R.; Saylor, J. E.; Horton, B. K.

    2013-12-01

    The uplift history of the Central Andean Plateau (CAP) presents challenges to paleoelevation research with both the rate and timing of uplift debated. Two end-member models have been proposed: 1) gradual surface uplift driven primarily by tectonic shortening (e.g., Barnes and Ehlers, 2009); and 2) rapid uplift in the late Miocene driven primarily by convective removal of dense lower lithosphere (e.g., Garzione et al., 2008). Recently acquired stable isotope and paleotemperature data present a more complex picture of CAP uplift, with multiple spatially and temporally separate uplift pulses (e.g., Quade et al., 2011; Saylor et al., 2012; Leier et al., 2013). In particular, Quade et al. (2011) and Saylor et al. (2012) suggest that the southern and northern CAP may have been uplifted in the early Oligocene and early Miocene, respectively; earlier than the central Altiplano implying an 'edge-to-center' progression of uplift. Determining the rates, timing, and spatial patterns of uplift is hindered by the complex array of factors that influence paleoelevation proxies. While the isotopic composition in rising air masses, precipitation and surface water shows a systematic depletion of 18O and D at higher elevations, this lapse rate may have varied through time due to changes in topography or climate (e.g., Insel et al., 2012). Further complications arise when using carbonates as a proxy record because the fractionation factor between surface water and carbonate depends on the temperature of crystallization which is, in turn, also dependent primarily on elevation. Here we present new deuterium isotopic analyses of volcanic glass in the Ayacucho Basin (13.15° S, 74.2° W), central Peru. The Ayacucho Basin is located north of the Altiplano at 2.7-3.7 km elevation, north of the Abancay Deflection. Volcanic glass is well suited for this study because once hydrated, the isotopic composition of the waters of hydration remains distinct from the isotopic composition of modern

  3. Identification of the Calderas for Major Ignimbrites of the Altiplano-Puna Volcanic Complex, Central Andes, Including Two New Super-eruptions

    NASA Astrophysics Data System (ADS)

    Ort, M. H.; de Silva, S. L.; Jiménez, N.

    2008-12-01

    The Neogene ignimbrite flare-up in the Altiplano-Puna Volcanic Complex (APVC) in the central Andes produced calderas and ignimbrites covering >70,000 km2 in Chile, Bolivia, and Argentina and totaling >11,000 km3 of magma. One of the questions related to this extraordinary occurrence is how long it took for these ignimbrites to be emplaced. In an effort to determine this, we have combined field correlations, high-precision 40Ar/39Ar dating, anisotropy of magnetic susceptibility (AMS) and characteristic remanent magnetism (ChRM) to constrain the dates of the eruptions. Herein we present the paleomagnetic data and preliminary interpretations, including the definition of two new super-eruptions in the APVC (including the youngest yet identified in the APVC). Several ignimbrites occupy similar stratigraphic positions. The Pastos Grandes and Tara Ignimbrites erupted 2.8-3.5 Ma, while the Chuhuilla, Alota, and Guacha Ignimbrites date between 5.3 and 5.6 Ma. The Pastos Grandes and Tara Ignimbrites have similar ChRM directions. The ChRM directions of the Alota and Guacha Ignimbrites are clearly distinct but the Chuhuilla Ignimbrite data have very large dispersion. The thermal demagnetization reveals a single component in nearly all the samples, which may indicate that the ignimbrites were emplaced above the magnetite Curie temperature. Current efforts center on refining and reducing the errors on the ChRM directions. AMS was used to determine flow directions and thus define the source areas for ignimbrites. The 3.51 Ma Tara Ignimbrite, first recognized as ponded ignimbrite in La Pacana caldera and thought to be erupted from there, is sourced in the Guacha caldera of Bolivia, likely from the western dome complex, which yields similar dates. Great thicknesses of Tara Ignimbrite are ponded within the Guacha caldera, and also around Cerro Zapaleri. This is the youngest super-eruption in the central APVC. The Pastos Grandes caldera was previously thought to have formed during

  4. Vivid valleys, pallid peaks? Hypsometric variations and rural–urban land change in the Central Peruvian Andes

    PubMed Central

    Haller, Andreas

    2012-01-01

    What happens to the land cover within the hinterland's altitudinal belts while Central Andean cities are undergoing globalization and urban restructuring? What conclusions can be drawn about changes in human land use? By incorporating a regional altitudinal zonation model, direct field observations and GIS analyses of remotely sensed long term data, the present study examines these questions using the example of Huancayo Metropolitano – an emerging Peruvian mountain city of 420,000 inhabitants, situated at 3260 m asl in the Mantaro Valley. The study's results indicate that rapid urban growth during the late 1980s and early 1990s was followed by the agricultural intensification and peri-urban condominization at the valley floor (quechua) – since the beginning of Peru's neoliberal era. Moreover, regarding the adjoining steep slopes (suni) and subsequent grassland ecosystems (puna), the research output presents land cover change trajectories that clearly show an expansion of human land use, such as reforestation for wood production and range burning for livestock grazing, even at high altitudes – despite rural–urban migration trends and contrary to several results of extra-Andean studies. Consequently, rural–urban planners and policy makers are challenged to focus on the manifold impacts of globalization on human land use – at all altitudinal belts of the Andean city's hinterland: toward sustainable mountain development that bridges the social and physical gaps – from the bottom up. PMID:23564987

  5. Coastal, valley, and oasis interaction: impact on the evolution of ancient populations in the South Central Andes.

    PubMed

    Varela, Héctor H; Cocilovo, Jose A; Fuchs, María L; O'Brien, Tyler G

    2014-12-01

    The existing biocultural links are analyzed among ancient inhabitants of the Cochabamba valleys (Bolivia) from the Formative and Tiwanaku periods, coastal and inland Azapa region (Chile) from the Late Archaic to the Late periods, and the Atacama Desert oases (Chile) from the Formative period to the time of European contact. Craniometric information obtained from a sample of 565 individuals from different sites of the studied regions was evaluated using methods derived from quantitative genetics and multivariate statistical analysis techniques. It is shown that during the Formative and Tiwanaku periods inhabitants of the Cochabamba valleys maintained contact with the population of northern Chile. This contact was more fluid with the people from the interior valley of Azapa than it was with the settlers of San Pedro Atacama (SPA). An important biological affinity in the Late Period between the inhabitants of the Azapa valley and the late SPA groups is also examined. The Late-Inca Catarpe SPA sample shows a broad genetic variability shared with the majority of the groups studied. The results reaffirm the differences between the coastal and interior Azapa valley groups and strengthen the hypothesis of two pathways to populating the south central Andean area. The divergence observed among subpopulations can be explained by the spatiotemporal dispersion between them, genetic drift dispersion compensated by the action of gene flow, and cultural norms that regulate within group mating. PMID:25234247

  6. Preliminary Depositional and Provenance Records of Mesozoic Basin Evolution and Cenozoic Shortening in the High Andes, La Ramada Fold-Thrust Belt, Southern-Central Andes (32-33°S)

    NASA Astrophysics Data System (ADS)

    Mackaman-Lofland, C.; Horton, B. K.; Fuentes, F.; Constenius, K. N.; McKenzie, R.; Alvarado, P. M.

    2015-12-01

    The Argentinian Andes define key examples of retroarc shortening and basin evolution above a zone of active subduction. The La Ramada fold-thrust belt (RFTB) in the High Andes provides insights into the relative influence and temporal records of diverse convergent margin processes (e.g. flat-slab subduction, convergent wedge dynamics, structural inversion). The RFTB contains Mesozoic extensional basin strata deformed by later Andean shortening. New detrital zircon U-Pb analyses of Mesozoic rift sediments reveal: (1) a dominant Permo-Triassic age signature (220-280 Ma) associated with proximal sources of effective basement (Choiyoi Group) during Triassic synrift deposition; (2) upsection younging of maximum depositional ages from Late Triassic through Early Cretaceous (230 to 100 Ma) with the increasing influence of western Andean arc sources; and (3) a significant Late Cretaceous influx of Paleozoic (~350-550 Ma) and Proterozoic (~650-1300 Ma) populations during the earliest shift from back-arc post-extensional subsidence to upper-plate shortening. The Cenozoic detrital record of the Manantiales foreland basin (between the Frontal Cordillera and Precordillera) records RFTB deformation prior to flat-slab subduction. A Permo-Triassic Choiyoi age signature dominates the Miocene succession, consistent with sources in the proximal Espinacito range. Subordinate Mesozoic (~80-250 Ma) to Proterozoic (~850-1800 Ma) U-Pb populations record exhumation of the Andean magmatic arc and recycling of different structural levels in the RFTB during thrusting/inversion of Mesozoic rift basin strata and subjacent Paleozoic units. Whereas maximum depositional ages of sampled Manantiales units cluster at 18-20 Ma, the Estancia Uspallata basin (~50 km to the south) shows consistent upsection younging of Cenozoic populations attributed to proximal volcanic centers. Ongoing work will apply low-temperature thermochronology to pinpoint basin accumulation histories and thrust timing.

  7. Expanding Geophysical and Geochemical Investigation of Causes of Extraordinary Unrest at the Laguna del Maule (Rhyolitic) Volcanic Field, Southern Andes, Chile

    NASA Astrophysics Data System (ADS)

    Singer, B. S.

    2014-12-01

    The Laguna del Maule Volcanic Field, Chile, includes an unusually large and recent concentration of silicic eruptions. Since 2007 the crust here has been inflating at an astonishing rate of 25 cm/yr. Findings thus far lead to the hypothesis that the silicic vents have tapped an extensive layer of crystal-poor, rhyolitic melt that began to form atop a magmatic mush zone that was established by ~20 ka with a renewed phase of rhyolite eruptions during the Holocene. Modeling of surface deformation, magnetotelluric data, and gravity changes suggest that magma is currently intruding at a depth of ~5 km. Swarms of volcano-tectonic and long period earthquakes, mostly of M < 2, have occurred beneath the most recent rhyolite coulees on the southwestern and southern margins of the 20 km diameter ring of silicic vents. With support from the US NSF and the Chilean government (SERNAGEOMIN and OVDAS) we are seizing the unique opportunity to investigate, over the next 5 years, the dynamics of this large rhyolitic system while magma migration, reservoir growth, and crustal deformation are actively underway. This collaboration involves scientists and students at: University of Wisconsin-Madison, Georgia Tech, Cornell, University of Alberta, Simon Fraser University, University of Chile-Santiago, CONICET/University of San Juan-Argentina, Nanyang Technological University-Singapore, SERNAGEOMIN, OVDAS, USGS, and SEGEMAR-Argentina. Team members will be introduced in this presentation. Our approach includes augmenting the OVDAS array of 6 permanent seisic stations with 40 additional instruments to conduct tomographic, receiver function and ambient noise studies. We continue to collect 4-D gravity data from 37 stations. Surface deformation is monitored via cGPS at 5 permanent receivers and InSAR data. A magnetotelluric survey across the Andes at 36o S is planned. Geochemical studies include mineral zoning and U-Th disequilibrium of zircons to constrain the timing of magma intrusion and

  8. New stratigraphic, chronologic, and magnetic fabric constraints for Neogene and Quaternary ignimbrites in the Central Andes (South Peru)

    NASA Astrophysics Data System (ADS)

    De La Rupelle, A.; Thouret, J. C.; Cubukcu, H. E.; Jicha, B.; Bréard, E.; Gerbe, M.-C.; Le Pennec, J.-L.; Diot, H.; Boivin, P.

    2012-04-01

    Central Andean deformation history in southern Peru is recorded in Neogene volcanic units of Ocoña and Cotahuasi canyons that cut across the western Cordillera. Acceleration (<25 Ma) of uplift in the region is reflected in the Neogene epiclastic deposits with interspersed and subsequent rhyolitic ignimbrites between 24.6 and 1.37 Ma. Large-volume (>100 km3) Nazca (c.24.6 Ma), Alpabamba (19.4-18.0 Ma), and Huaylillas (14.25-12.7 Ma) ignimbrite sheets preceded the canyon incision, whereas sheets of smaller volume (<50 km3), Caraveli (9.5-8.9 Ma), Lower (5.13-3.6 Ma) and Upper Sencca (c.2 Ma) and Las Lomas (c.1.56-1.37 Ma), were deposited during canyon incision and are interspersed with Lower and Upper Barroso lava flows. The Alpabamba compound ignimbrite sheets comprise a vitrophyre at the base, grading into a strongly welded, eutaxitic, crystal-rich facies overlain by a thick, multi-bedded ash-flow tuff and a lithic-rich, indurated flow unit. The Huaylillas ignimbrite sheet comprises a strongly welded, crystal-rich, lithic-poor, columnar lithofacies, with devitrified pumice. The Caraveli ignimbrite sheet has a jointed vitrophyre overlain by a welded, blocky, crystal-rich flow unit. A vacuolar, saccharolytic unit forms the top of the sequence. The Lower Sencca ignimbrite sheet comprises of a basal vitrophyre and a slightly welded, fibrous pumice-rich flow unit, which grades into a welded, vapor-phase unit that contains more crystals than pumice and lithics. The Upper Sencca ignimbrite sheet consists of a black vitrophyre, grading into a strongly welded, crystal-rich, eutaxitic cooling unit. The latter is capped by a slightly welded unit, and an indurated pumice-rich, crystal-poor vapour-phase facies. Quaternary valley-fill termed Las Lomas consists of unwelded, crystal-poor pumice-flow deposits. Eighteen new 40Ar/39Ar analyses have been carried out on feldspar/glass separates from pumice and lavas. Results for the Caraveli ignimbrite (9.35±0.06 Ma), Upper Barroso

  9. Mapping South American Summer Monsoon Changes during Heinrich Event 1 and the LGM: Insights from New Paleolake Records from the Central Andes

    NASA Astrophysics Data System (ADS)

    Chen, C. Y.; McGee, D.; Quade, J.

    2015-12-01

    Cave stalagmite records show strong evidence of abrupt changes in summer monsoons during Heinrich events, but we lack rigorous constraints on the amount of wetting or drying occurring in monsoon regions. Studies on shoreline deposits of closed-basin lakes can establish quantitative bounds on water balance changes through mapping-based estimates of lake volume variations. We present new dating constraints on lake level variations in Agua Caliente I and Laguna Loyoques, two closed-basin, high-altitude paleolakes on the Altiplano-Puna plateau of the Central Andes (23.1°S, 67.4°W, 4250 masl). Because this area receives >70% of its total annual precipitation during austral summer, the region is ideally suited to capture a pure response to changes in the South American summer monsoon (SASM). The plateau is home to several small (<40 km2) lakes surrounded by well-preserved paleoshorelines that indicate past wetter conditions. Agua Caliente I is unique, having multiple shorelines encrusted with biologically-mediated calcium carbonate "tufa" deposits. Initial U-Th dating of these massive shoreline tufas reveals that these deposits are dateable to within ±50 to 300 years due to high U concentrations and low initial Th content (as indicated by high 230Th/232Th). Our U-Th dates show that Agua Caliente I was greater in lake surface area during two periods: 17.5-14.5 kyrs BP, coincident with Heinrich Event 1 (HE1), and 24-23 kyrs BP, roughly coincident with the Last Glacial Maximum (LGM). At these times, Agua Caliente I also overflowed into a neighboring lake basin (Loyoques) through an 8-km long southeast-trending stream channel. Thus, during HE1 and the LGM, the lake was ~9 times larger in surface area relative to modern. Hydrologic modeling constrained by paleotemperature estimates is used to provide bounds for these past precipitation changes. We also tentatively explore physical mechanisms linking Heinrich events and the regional hydroclimate by comparing freshwater

  10. Eruption and Degassing Processes in a Supervolcanic System: The Volatile Record Preserved in Melt Inclusions from the 3.49Ma Tara Ignimbrite in the Central Andes

    NASA Astrophysics Data System (ADS)

    Grocke, S.; de Silva, S. L.; Schmitt, A. K.; Wallace, P. J.

    2010-12-01

    Analysis of H2O and CO2 in quartz and sanidine-hosted melt inclusions from one of the youngest supervolcanic eruptions in the Altiplano Puna Volcanic Complex (APVC) in the Central Andes provides information on crystallization depths and eruption and degassing processes. At least 740 km3 of high-K, metaluminous, rhyodacite to rhyolite magma erupted from the Guacha Caldera in southwest Bolivia, producing three phases of the 3.49 Ma Tara Ignimbrite: a Plinian fall-deposit, an extensive ignimbrite, and several post-caldera domes. Infrared spectroscopic analyses of quartz-hosted melt inclusions from Tara Plinian pumice have H2O contents of ~4.5 wt % and variable CO2 contents (110-300 ppm), corresponding to vapor saturation pressures up to 180 MPa. In contrast, sanidine-hosted melt inclusions from the Plinian-fall deposit contain bubbles, lower water contents (1.4-2.2 wt %) and lower CO2 (87-143 ppm). These vesiculated melt inclusions and low volatile contents suggest that the sanidine crystals leaked on their ascent to the surface and therefore do not record accurate pre-eruptive melt volatile contents. In contrast, quartz-hosted melt inclusions from post-caldera dome samples contain lower H2O contents of 2.5-3.5 wt % (average 2.9 wt %) and no detectable CO2, corresponding to vapor saturation pressures of 50-90 MPa. These data indicate that the preeruptive plinian stage Tara magma was vapor saturated at the time of melt inclusion entrapment and stored between 5-6 km, while those from the post-caldera domes were trapped at 2-3 km. Differences in CO2 between Plinian and dome melt inclusions require that the post-caldera dome quartzes represent a different generation of crystals that grew as the magma slowly rose and progressively degassed at 2-3 km. During this shallow crystallization, the magma evolved further and eventually fed the post-caldera domes, one of which is a high-Si rhyolite. Consistent with this interpretation, melt inclusions from post-caldera dome samples

  11. Natural dam failure in the eastern slope of the Central Andes of Argentina. Numerical modelling of the 2005 Santa Cruz river outburst flood

    NASA Astrophysics Data System (ADS)

    Penna, I.; Daicz, S.; Zlotnik, S.; Derron, M.-H.; Jaboyedoff, M.

    2012-04-01

    In the Central Andes of Argentina, ephemeral river blockage due to landslides deposition are common phenomena. During the first fortnight of January 2005, 11.5 * 106m3 of rock collapsed from the east slope of the Santa Cruz valley (San Juan province, Argentina). The rock mass displaced from 4300 m a.s.l., down to the valley bottom, at 2900 m a.s.l., and ran up the opposite flank of the valley. This produced the blockage of the Santa Cruz river and generated the Los Erizos lake. The rapid snow melting during the spring season caused the increase of the water level of the reservoir, leading to a process of overtopping on November 12th of 2005. 30 * 106m3 of water were released from the reservoir and the consequent outburst flood displaced along 250 km. From local reports of arrival times, we estimated that the outburst flood reduced its velocity from around 40 km/h near the source area to 6 km/h in its distal section. A road, bridges, and a mining post where destroyed. 75 tourists had to be rescued from the mountains using helicopters, and people from two localities had to be evacuated. Near its distal part, the flood damaged the facilities of the Caracoles power dam, which was under construction, and its inauguration had to be delayed one year due to the damage. The outburst flood produced changes in the morphology of the valley floor along almost all its path (erosion of alluvial fans, talus and terraces, and deposition of boulders). The most significant changes occurred in the first 70 km, especially upstream narrow sections, showing the importance of the backwater effects due to hydraulic ponding. In this work we carried out numerical simulations to obtain the velocity patterns of the flood, and compared them with those obtained from local reports. Furthermore, we analyze the relationship between the dynamics of the flood with the patterns of erosion and deposition near the source area.

  12. Modelling the hydrological response of debris-free and debris-covered glaciers to present climatic conditions in the semiarid Andes of central Chile

    NASA Astrophysics Data System (ADS)

    Ayala, Alvaro; Pellicciotti, Francesca; MacDonell, Shelley; McPhee, James; Vivero, Sebastián; Campos, Cristián; Egli, Pascal

    2016-04-01

    We investigate the main contributors to runoff of a 62 km2 glacierized catchment in the semiarid Andes of central Chile, where both debris-free and debris-covered glaciers are present, combining an extensive set of field measurements, remote sensing products and an advanced glacio-hydrological model (TOPKAPI-ETH). The catchment contains two debris-free glaciers reaching down to 3900 m asl (Bello and Yeso Glaciers) and one debris-covered avalanche-fed glacier reaching to 3200 m asl (Piramide Glacier). A unique dataset of field measurements collected in the ablation seasons 2013-14 and 2014-15 included four automatic weather stations, manual measurements of snow depth and debris cover thickness, discharge measurements at glaciers outlets, photographic monitoring of surface albedo as well as ablation stakes measurements and snow pits. TOPKAPI-ETH combines physically-oriented parameterizations of snow and ice ablation, gravitational distribution of snow, snow albedo evolution, glacier dynamics, runoff routing and the ablation of debris-covered ice.We obtained the first detailed estimation of mass balance and runoff contribution of debris-covered glaciers in this mountainous region. Results show that while the mass balance of Bello and Yeso Glaciers is mostly controlled by air temperature lapse rates, the mass balance of Piramide Glacier is governed by debris thickness and avalanches. In fact, gravitational distribution by avalanching on wet years plays a key role and modulates the mass balance gradient of all glaciers in the catchment and can turn local mass balance from negative to positive. This is especially the case for Piramide Glacier, which shows large amounts of snow accumulation below the steep walls surrounding its upper area. Despite the thermal insulation effect of the debris cover, the contribution to runoff from debris-free and debris-covered glaciers is similar, mainly due to elevation differences. At the catchment scale, snowmelt represents more than 60

  13. The role of changing geodynamics in the progressive contamination of Late Cretaceous to Late Miocene arc magmas in the southern Central Andes

    NASA Astrophysics Data System (ADS)

    Jones, Rosemary E.; Kirstein, Linda A.; Kasemann, Simone A.; Litvak, Vanesa D.; Poma, Stella; Alonso, Ricardo N.; Hinton, Richard

    2016-10-01

    The tectonic and geodynamic setting of the southern Central Andean convergent margin changed significantly between the Late Cretaceous and the Late Miocene, influencing magmatic activity and its geochemical composition. Here we investigate how these changes, which include changing slab-dip angle and convergence angles and rates, have influenced the contamination of the arc magmas with crustal material. Whole rock geochemical data for a suite of Late Cretaceous to Late Miocene arc rocks from the Pampean flat-slab segment (29-31 °S) of the southern Central Andes is presented alongside petrographic observations and high resolution age dating. In-situ U-Pb dating of magmatic zircon, combined with Ar-Ar dating of plagioclase, has led to an improved regional stratigraphy and provides an accurate temporal constraint for the geochemical data. A generally higher content of incompatible trace elements (e.g. Nb/Zr ratios from 0.019 to 0.083 and Nb/Yb from 1.5 to 16.4) is observed between the Late Cretaceous (~ 72 Ma), when the southern Central Andean margin is suggested to have been in extension, and the Miocene when the thickness of the continental crust increased and the angle of the subducting Nazca plate shallowed. Trace and rare earth element compositions obtained for the Late Cretaceous to Late Eocene arc magmatic rocks from the Principal Cordillera of Chile, combined with a lack of zircon inheritance, suggest limited assimilation of the overlying continental crust by arc magmas derived from the mantle wedge. A general increase in incompatible, fluid-mobile/immobile (e.g., Ba/Nb) and fluid-immobile/immobile (e.g., Nb/Zr) trace element ratios is attributed to the influence of the subducting slab on the melt source region and/or the influx of asthenospheric mantle. The Late Oligocene (~ 26 Ma) to Early Miocene (~ 17 Ma), and Late Miocene (~ 6 Ma) arc magmatic rocks present in the Frontal Cordillera show evidence for the bulk assimilation of the Permian-Triassic (P

  14. A Holocene Lake Record from Laguna Del Maule (LdM) in the Chilean Andes: Climatic and Volcanic Controls on Lake Depositional Dynamics

    NASA Astrophysics Data System (ADS)

    Valero-Garces, B. L.; Frugone Alvarez, M.; Barreiro-Lostres, F.; Carrevedo, M. L.; Latorre Hidalgo, C.; Giralt, S.; Maldonado, A.; Bernárdez, P.; Prego, R.; Moreno-Caballud, A.

    2014-12-01

    Central Chile is a tectonically active, drought-prone region sensitive to latitudinal variations in large-scale cold fronts associated with fluctuations of the Pacific subtropical high. Holocene high-resolution records of climate and volcanic events could help inform more on the frequency of extensive droughts as well as volcanic and seismic hazards. LdM is a high altitude, volcanic lake located in the Transition Southern Volcanic Zone (~36°S, 2200 m.a.s.l). The LdM volcanic field is a very seismically and volcanically active zone in the Andes, with several caldera-forming eruptions over the last 1.5 Ma, and intense postglacial activity. In 2013, we recovered over 40 m of sediment cores at four sites of LdM and collected > 20 km of seismic lines. The cores were imaged, their physical and geochemical properties analysed with a Geotek MSCL and XRF scanner respectively, and sampled for TOC, TIC, TS, TN, BioSi, and bulk mineralogy. The chronology was constructed with a Bayesian age-depth model including 210Pb-137Cs, the Quizapú volcanic ash (1932 AD) and 17 AMS 14C dates. The 4.8 m long composite sequence spans the Late glacial and Holocene.Sediments are massive to banded, quartz and plagioclase-rich silts with variable diatom (BioSi, 15- 30 %) and organic matter content (TOC, 1-5 %). Four main units have been defined based on sedimentological and geochemical composition. The transition from Unit 4 to 3 is ascribed to the onset of the Holocene; Unit 2 spans the mid Holocene, and Unit 1 the last 4 ka. Higher (lower) TOC, Br/Ti and Fe/Mn ratios in units 1 and 3 (2 and 4) suggest higher (lower) organic productivity in the lake and dominant oxic (anoxic) conditions at the bottom of the lake. Up to 17 ash and lapilli layers mark volcanic events, mostly grouped in units 1 and 3. Periods of higher lake productivity (units 1 and 3) are synchronous to higher frequency of volcanic events. Some climate transitions (LIA, 4ka, 8ka and 11ka) are evident in the LdM sequence

  15. Andes Altiplano, South America

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Looking westward over the Andes Altiplano, (14.S, 72.5W) this panoramic view shows details of the deep river gorges cut into the mountains as they rose to their present heights of over 10,000 to 13,000 ft. over the past 20 million years. The eastern slopes of the Andes are heavily forested and form the headwaters of the Amazon River drainage basin. Smoke from logging or land clearing operations can be seen in the lower river valleys.

  16. Evaluation of Little Ice Age cooling in Western Central Andes, suggested by paleoELAs, in contrast with global warming since late 19th century deduced from instrumental records

    NASA Astrophysics Data System (ADS)

    Ubeda, Jose; Palacios, David; Campos, Néstor; Giraldez, Claudia; García, Eduardo; Quiros, Tatiana

    2015-04-01

    This paper attempts to evaluate climate cooling (°C) during the glacial expansion phases using the product GTV•ΔELA, where GTV is the vertical air temperature gradient (°C/m) and ΔELA (m) the difference in level observed between the Equilibrium Line Altitude (ELA) reconstructions for current and past glaciers. With this aim the Area x Altitude Balance Ratio-(AABR) method was used to produce reconstructions of present ELAs (2002-2010) and paleoELAs corresponding to the last glacier advance phase. The reconstructions were produced in three study areas located along a N-S transect of the western cordillera in the Central Andes: the south-western sector of the Nevado Hualcán (9°S, 77°W; Giráldez 2011); the southern slope of the Cordillera Pariaqaqa (12°S, 76°W; Quirós, 2013) and the NW, NE, SE and SW quadrants of the Nevado Coropuna (16°S, 72°W; García 2013; Úbeda 2011; Campos, 2012). The three mountains exceed 6000 m altitude, their summit areas are covered by glaciers, and on their slopes there are existing well-conserved moraines deposited by the last advances near the present front of the ice masses. Although there are no absolute dates to confirm this hypothesis, it has been assumed that the last glacial advances occurred during the Little Ice Age (LIA), which the oxygen isotopes of the Nevado Huascarán (9°S, 77°W) date to the period 1500-1890. For the Hualcán and Pariaqaqa the mean global value of the Earth's GTV (6.5°C/km) was used, considered valid for the Tropics. On the Coropuna a GTV=8.4°C/km was used, based on high resolution sensors installed in situ since 2007 (Úbeda 2011). This gradient is approaching the upper limit of the dry adiabatic gradient (9.8°C/km), as the Coropuna region is more arid than the other case study areas. The climate cooling estimates deduced from the product GTV•ΔELA were compared with the global warming shown by the 1880-2012 series, ΔT=0.85°C, and 1850/1900-2003/2012, ΔT=0.78°C. The differences are

  17. Present and future water resources supply and demand in the Central Andes of Peru: a comprehensive review with focus on the Cordillera Vilcanota

    NASA Astrophysics Data System (ADS)

    Drenkhan, Fabian; Huggel, Christian; Salzmann, Nadine; Giráldez, Claudia; Suarez, Wilson; Rohrer, Mario; Molina, Edwin; Montoya, Nilton; Miñan, Fiorella

    2014-05-01

    Glaciers have been an important element of Andean societies and livelihoods as direct freshwater supply for agriculture irrigation, hydropower generation and mining activities. Peru's mainly remotely living population in the Central Andes has to cope with a strong seasonal variation of precipitations and river runoff interannually superimposed by El Niño impacts. Direct glacier and lake water discharge thus constitute a vital continuous water supply and represent a regulating buffer as far as hydrological variability is concerned. This crucial buffer effect is gradually altered by accelerated glacier retreat which leads most likely to an increase of annual river runoff variability. Furthermore, a near-future crossing of the 'peak water' is expected, from where on prior enhanced streamflow decreases and levels out towards a new still unknown minimum discharge. Consequently, a sustainable future water supply especially during low-level runoff dry season might not be guaranteed whereas Peru's water demand increases significantly. Here we present a comprehensive review, the current conditions and perspectives for water resources in the Cusco area with focus on the Vilcanota River, Cordillera Vilcanota, Southern Peru. With 279 km2 the Cordillera Vilcanota represents the second largest glacierized mountain range of the tropics worldwide. Especially as of the second half of the 1980s, it has been strongly affected by massive ice loss with around 30% glacier area decline until present. Furthermore, glacier vanishing triggers the formation of new lakes and increase of lake levels and therefore constitutes determining hazardous drivers for mass movements related to deglaciation effects. The Vilcanota River still lacks more profound hydrological studies. It is likely that its peak water has already been or might be crossed in near-future. This has strong implications for the still at 0.9% (2.2%) annually growing population of the Cusco department (Cusco city). People mostly

  18. Palaeoclimate reconstructions from lacustrine terraces and lake-balance modeling in the southern central Andes: New insights from Salar de Pocitos (Salta Province, Argentina)

    NASA Astrophysics Data System (ADS)

    Bekeschus, Benjamin; Bookhagen, Bodo; Strecker, Manfred R.; Freymark, Jessica; Eckelmann, Felix; Alonso, Ricardo

    2013-04-01

    The arid Puna Plateau in the southern central Andes of NW-Argentina constitutes the southern part of Earth's second largest orogenic plateau. Numerous internally drained basins are restricted by ranges that peak 5-6 km above sea level, creating a compressional basin and range morphology. The conspiring effects of this structurally controlled topography and the high degree of aridity have resulted in low stream power of the fluvial network and internally drained basins. A steep rainfall gradient exists across this area ranging from a humid Andean foreland (>1m/yr annual rainfall) to progressively drier areas westwards. At the present-day, the interior of the plateau is widely characterized by < 0.1m/yr annual rainfall and high evaporation rates. Thus continuous lacustrine archives are limited and sediments are dominated by evaporites. Several closed basins contain vestiges of moister conditions from past pluvial periods. For example, the staircase morphology of lacustrine shorelines and abrasion platforms in the distal sectors of alluvial fans and pediments at Salar de Pocitos (24.5°S, 67°W, 3650 m asl) records repeated former lake highstands. This intermontane basin has existed since the late Tertiary, constituting a 435 km² salt flat in the region of Salta, NW Argentina. Comparison with palaeoclimate records from the neighboring Salar de Atacama suggests that the terrace systems at Salar de Pocitos were formed during the Late Pleistocene and early Holocene. Here we report on our preliminary results of the extent of several terrace generations in this region. We mapped terraces in the field and on satellite images and determined their elevations during a high-resolution DGPS field survey. Our analysis reveals 3-4 distinct terrace levels associated with individual lake-level highstands. However, basin-wide correlation is difficult due to ongoing tectonism and differential tilting of the basin. The highest lake terrace, ca. 25 m above modern base level, locally

  19. Correlation and Analysis of Volcanic Ash in Marine Sediments From the Peru Margin: Explosive Volcanic Cycles of the North-Central Andes

    NASA Astrophysics Data System (ADS)

    Hart, D.; Miller, J.

    2003-12-01

    To decipher the episodicity of explosive volcanic activity in the North-Central Andes, we have measured the thickness and calculated the volume of ash layers from sites drilled along the Peru margin during Leg 201 of the Ocean Drilling Program (ODP). The geographic distribution of the sites (over 3 degrees of latitude and from 50 to 300 km offshore) and correlation of ash units between sites form the basis for minimal estimates of explosive volcanic activity in the region (only eruptions large enough to deposit ash in excess of 100 km from source are represented). Pouclet et al., (1990), estimated the minimum explosive activity along the Andean Arc from ash-bearing sediments and ash layers within cores from sites along the Peru margin collected during ODP Leg 112. As a result of higher recovery (as much as ten times more core recovery in many intervals) and decreased disturbance in cores recovered during Leg 201, our documentation of ash content in cores from Leg 201 has led to a more complete record of the explosive volcanic activity along the Andean Arc. For example, Pouclet, et al., (1990), reports four ash layers from Sites 680 and 684, whereas we have documented fourteen ash layers from cores recovered from the same locations (Sites 1228 and 1227, respectively). Our stratigraphic record agrees with Pouclet, et al., (1990), suggesting that explosive activity began in the early Eocene ( ˜35Ma) and continued with explosive pulses during the Miocene. The greatest explosive activity occurred within the past 5 million years, with peak activity in the late Pliocene to early Pleistocene. Based on petrographic and geochemical analysis, most of the volcanic ash within cores from Leg 201 was derived from the Andean volcanic arc. These plinian eruptions produced acidic glasses and ash layers with abundant feldspar, hornblende, and biotite. Pouclet, et al., (1990), reports a transition from andesitic volcanism in the Middle to Late Miocene to a more shoshonitic

  20. Reconstructing the annual mass balance of the Echaurren Norte glacier (Central Andes, 33.5° S) using local and regional hydroclimatic data

    NASA Astrophysics Data System (ADS)

    Masiokas, Mariano H.; Christie, Duncan A.; Le Quesne, Carlos; Pitte, Pierre; Ruiz, Lucas; Villalba, Ricardo; Luckman, Brian H.; Berthier, Etienne; Nussbaumer, Samuel U.; González-Reyes, Álvaro; McPhee, James; Barcaza, Gonzalo

    2016-04-01

    Despite the great number and variety of glaciers in southern South America, in situ glacier mass-balance records are extremely scarce and glacier-climate relationships are still poorly understood in this region. Here we use the longest (> 35 years) and most complete in situ mass-balance record, available for the Echaurren Norte glacier (ECH) in the Andes at ˜ 33.5° S, to develop a minimal glacier surface mass-balance model that relies on nearby monthly precipitation and air temperature data as forcing. This basic model is able to explain 78 % of the variance in the annual glacier mass-balance record over the 1978-2013 calibration period. An attribution assessment identified precipitation variability as the dominant forcing modulating annual mass balances at ECH, with temperature variations likely playing a secondary role. A regionally averaged series of mean annual streamflow records from both sides of the Andes between ˜ 30 and 37° S is then used to estimate, through simple linear regression, this glacier's annual mass-balance variations since 1909. The reconstruction model captures 68 % of the observed glacier mass-balance variability and shows three periods of sustained positive mass balances embedded in an overall negative trend over the past 105 years. The three periods of sustained positive mass balances (centered in the 1920s-1930s, in the 1980s and in the first decade of the 21st century) coincide with several documented glacier advances in this region. Similar trends observed in other shorter glacier mass-balance series suggest that the Echaurren Norte glacier reconstruction is representative of larger-scale conditions and could be useful for more detailed glaciological, hydrological and climatological assessments in this portion of the Andes.

  1. Tectonic deformation of the Andes and the configuration of the subducted slab in central Peru: Results from a micro-seismic experiment

    NASA Technical Reports Server (NTRS)

    Suarez, G.; Gagnepain, J. J.; Cisternas, A.; Hatzfeld, D.; Molnar, P.; Ocola, L.; Roecker, S. W.; Viode, J. P.

    1983-01-01

    The vast majority of the microearthquakes recorded occurred to the east: on the Huaytapallana fault in the Eastern Cordillera or in the western margin of the sub-Andes. The sub-Andes appear to be the physiographic province subjected to the most intense seismic deformation. Focal depths for the crustal events here are as deep as 50 km, and the fault plane solutions, show thrust faulting on steep planes oriented roughly north-south. The Huaytapallana fault in the Cordillera Oriental also shows relatively high seismicity along a northeast-southwest trend that agrees with the fault scarp and the east dipping nodal plane of two large earthquakes that occurred on this fault in 1969. The recorded microearthquakes of intermediate depth show a flat seismic zone about 25 km thick at a depth of about 100 km. This agrees with the suggestion that beneath Peru the slab first dips at an angle of 30 deg to a depth of 100 km and then flattens following a quasi-horizontal trajectory. Fault plane solutions of intermediate depth microearthquakes have horizontal T axes oriented east-west.

  2. New evidence for late mesozoic-early Cenozoic evolution of the Chilean Andes in the upper Tinguiririca valley (35 °S), central Chile

    NASA Astrophysics Data System (ADS)

    Charrier, Reynaldo; Wyss, AndréR.; Flynn, John J.; Swisher, Carl C.; Norell, Mark A.; Zapatta, Franyo; McKenna, Malcolm C.; Novacek, Michael J.

    1996-11-01

    New geologic, paleontologic and isotopic geochronometric results from the Termas del Flaco region in the upper Tinguiririca River valley in central Chile demand considerable revision of the accepted geotectonic history of the Andean Main Range in this region. A diverse, transitional Eocene-Oligocene aged, land-mammal fauna was recovered from several sites in volcaniclastic sediments of the Coya-Machalí (=Abanico) Formation. Major results of our study include: 1) The 1000 + m thick studied deposits, previously attributed to the Cretaceous Colimapu Formation, belong to the Coya-Machalí (=Abanico) Formation. Radioisotopic data from levels immediately above (31.5 Ma) and below (37.S Ma) the fossiliferous horizon indicate a latest Eocene to early Oligocene age for the basal part of the formation and the fauna contained in it. 2) The fossiliferous unit rests with slight angular offset on different Mesozoic units: "Brownish-red Clastic Unit" (BRCU) and Baños del Flaco Formation; in a limited area it also overlies a white tuff dated at 104 Ma. 3) The contacts just discussed (none of which is attributable to faulting), demonstrate the existence of two, or possibly three, unconformities in the region. 4) Sedimentological criteria argue against reference of the BRCU to the Colimapu Formation, and imply correlation of the former unit to basal levels with in the late Cretaceous Neuquén Group of western Argentina. 5) The Coya-Machalí Formation, previously viewed as representing the western volcanic equivalent of Riográndico Supercycle deposits of western Argentino, is likely coeval to much younger units in that region such as the Agua de la Piedra Formation. 6) Paleomagnetic results from the fossil producing horizon indicate about 20 ° of post-early Oligocene, counterclockwise rotation. 7) Fossil mammals from the Coya-Machalí Formation near Termas del Flaco represent a distinct biochronologic interval not heretofore clearly recognized from elsewhere on the continent

  3. Facies and sedimentary environments of the cretaceous La Luna Formation in San Pedro Del Rio section, Venezuelan Andes: A multidisciplinary study

    SciTech Connect

    Boesi, H.T.R.; Lorente, M.A.; Mompart, L.; Murat, B.; Testamarck ); Facon, R. )

    1993-02-01

    Vertical variations in facies and sedimentary environments in an outcrop of the La Luna Formation in the Venezuela Andes were evaluated with an integrated study of sedimentology, micropaleontology, palynology, visual kerogen, organic geochemistry and field geology. Up to now, the La Luna Formation, main hydrocarbon source rock in the Maracaibo Basin, has been considered for calculations of oil generation as an homogeneous interval with similar properties across the basin. However, this study reveals important vertical variations in organic facies and sedimentary environments. The microfacies range from almost pure carbonate (recrystallized) mudstone to almost pure shale, with a varying organic content. An overall upward change from oxic to anoxic environments can be recognized, culminating in a chert-rich interval (Ftanita de Tachira Member). The total organic carbon content is high throughout, with the exception of low to moderate values in the chert. The organic matter is mature to postmature. Phosphatic intervals are also developed, supporting a model of platform-edge upwelling and high organic productivity. The presence of rare volcanic grains suggests comtemporaneous volcanic activity within adjacent areas (Colombian Andes ).

  4. Crustal Thickness in Northern Andes Using pP and sS Precursors at Teleseismic Distances

    NASA Astrophysics Data System (ADS)

    Aranda Camacho, N. M.; Assumpcao, M.

    2013-12-01

    The Andean belt is a result of the subduction of the Nazca plate beneath the South American continental plate. It has an extension of 8000 km from Venezuela to Tierra del Fuego. While the crustal-thickness is a well-known property in Southern and Central Andes, it is still poorly known in the Northern Andes (between 10°N and 4° S). The crustal thickness is a very important property to understand the crustal evolution such as in geodynamic models and in modeling wave-propagation in global and regional seismic studies. Due to the high seismic activity at intermediate depths in the Northern Andes, it is possible to use the teleseismic P-wave and S-wave trains to find the crustal-thickness. In this study, we analyze the reflections from the underside of the Moho for intermediate and deep earthquakes in the northern Andes recorded at teleseismic distances (between 40°- 85°), and estimate the crustal-thickness at the bounce points of the pP and sS wave by converting the delay time between the phases pP and pmP and also between sS and smS into crustal thickness. This method can be applied in zones with earthquakes having magnitude larger than 6 for that reason the Northern Andes is a favorable area to develop it. We analyzed five events from the Northern Andes with magnitude larger than 6 and deeper than 100 km. The crustal thickness was calculated using the P wave with the vertical component and the S wave using both transverse SH and radial SV components. We find that the crustal-thickness in this area varied from 27.9 × 2.4 km at (76.48 W, 4.82 N) to 55.7 × 5.2 km at (77.92 W, 2 S). Our results show a crustal-thickness consistent with a compilation made for a larger region that includes our research area, showing residuals between -4 km and 4 km in most of the bounce points . We are getting results in areas that have not been studied previously so it will help to increase the database of crustal-thicknesses for the Northern Andes.

  5. Gastrointestinal helminths of Commerson's dolphins Cephalorhynchus commersonii from central Patagonia and Tierra del Fuego.

    PubMed

    Berón-Vera, B; Pedraza, S N; Raga, J A; Gil de Pertierra, A; Crespo, E A; Alonso, M K; Goodall RNP

    2001-12-01

    The stomachs and intestines of 9 Commerson's dolphins incidentally caught in trawl nets in central Patagonia and 23 stranded on beaches in Tierra del Fuego were surveyed for helminth parasites. A total of 267 individuals belonging to 4 species of parasites (1 nematode, 3 digeneans) were found in the dolphins from the first area: Anisakis sp. (larvae type 1 = A. simplex), Braunina cordiformis, Hadwenius sp. and Pholeter gastrophilus. In the Tierra del Fuego dolphins, 142 specimens belonging to 3 species (2 nematodes, 1 digenean, 1 cestode) were found: A. simplex, Hadwenius sp. and Strobilocephalus triangularis. Only 2 of the helminth species were shared in the 2 study areas, A. simplex and Hadwenius sp., and both were more common in central Patagonia. Among the species, A. simplex was most prevalent and abundant in both study areas. In Tierra del Fuego, adults of A. simplex appeared in only 1 host. Hadwenius sp., P. gastrophilus and S. triangularis are new host records for Commerson's dolphin. Species diversity and species richness were low in both study areas. Helminth communities were more diverse in central Patagonia (t = 1.97, df = 258, p < 0.05) and species richness was higher in central Patagonia (S = 4). No differences in diversity were observed between females and males of central Patagonia (t = 1.97, df = 139, p < 0.05) and between females of central Patagonia and Tierra del Fuego. The results may suggest some differences in habitat use, diet and sex between Commerson's dolphin populations in the 2 study areas.

  6. Late Oligocene-Early Miocene compressional tectosedimentary episode and associated land-mammal faunas in the Andes of central Chile and adjacent Argentina (32 37°s)

    NASA Astrophysics Data System (ADS)

    Semper, Thierry; Marshall, Larry G.; Rivano, Sergio; Godoy, Estanislao

    1994-01-01

    A reassessment of the geologic and land-mammal fossil evidence used in attribution of a tectosedimentary episode in the Andes between 32 and 37°S to the Middle Eocene "Incaic tectonic phase" of Peru indicates that the episode occurred during Late Oligocene-Early Miocene times(~ 27-20 Ma). From west to east, three structural domains are recognized for this time span in the study area: a volcanic arc (Chile); a thin-skinned, E-verging fold-thrust belt (Cordillera Principal, Chile-Argentina border strip); and a foreland basin (Argentina). Initiation of thrusting in the Cordillera Principal fold-thrust belt produced the coeval initiation of sedimentation in the foreland basin of adjacent Argentina. This onset of foreland deposition postdates strata bearing a Divisaderan Land Mammal Age fauna (i.e. ~ 35-30 Ma) and is marked at ~ 36°30'S by the base of the "Rodados Lustrosos" conglomerates, which are conformably overlain by sedimentary rocks containing a Deseadan Land Mammal Age fauna (i.e. ~ 29-21 Ma). Geologic relationships between the thick volcanic Abanico (Coya-Machalí) and Farellones formations also demonstrate that this tectosedimentary episode practically ended at ~ 20 Ma at least in the volcanic arc, and was therefore roughly coeval with the major tectonic crisis (~ 27-19 Ma) known in northwestern Andean Bolivia some 1500 km to the north. This strongly suggests that a long, outstanding tectonic upheaval affected at least an extended 12-37°S segment of the Andean margin of South America during Late Oligocene and Early Miocene times.

  7. Geometry of the inverted Cretaceous Chañarcillo Basin based on 2-D gravity and field data - an approach to the structure of the western Central Andes of northern Chile

    NASA Astrophysics Data System (ADS)

    Martínez, F.; Maksymowicz, A.; Ochoa, H.; Díaz, D.

    2015-12-01

    This paper discusses an integrated approach that provides new ideas about the structural geometry of the NNE-striking, Cretaceous Chañarcillo Basin located along the eastern Coastal Cordillera in the western Central Andes of northern Chile (27-28° S). The results obtained from the integration of two transverse (E-W) gravity profiles with previous geological information show that the architecture of this basin is defined by a large NNE-SSE-trending and east-vergent anticline ("Tierra Amarilla Anticlinorium"), which is related to the positive reactivation of a former Cretaceous normal fault (Elisa de Bordos Master Fault). Moreover, intercalations of high and low gravity anomalies and steep gravity gradients reveal a set of buried, west-tilted half-grabens associated with a synthetic normal fault pattern. These results, together with the uplift and folding style of the Cretaceous synextensional deposits recognized within the basin, suggest that its structure could be explained by an inverted fault system linked to the shortening of pre-existing Cretaceous normal fault systems. Ages of the synorogenic deposits exposed unconformably over the frontal limb of the Tierra Amarilla Anticlinorium confirm a Late Cretaceous age for the Andean deformation and tectonic inversion of the basin.

  8. Geometry of the inverted Cretaceous Chañarcillo Basin based on 2-D gravity and field data. An approach to the structure of the western Central Andes of northern Chile

    NASA Astrophysics Data System (ADS)

    Martínez, F.; Maksymowicz, A.; Ochoa, H.; Díaz, D.

    2015-08-01

    This paper discusses an integrated approach that provides new ideas about the structural geometry of the NNE-striking, Cretaceous Chañarcillo Basin located along the eastern Coastal Cordillera in the western Central Andes of northern Chile (27-28° S). The results obtained from the integration of two transverse (E-W) gravity profiles with previous geological information, show that the architecture of this basin is defined by a large NNE-SSE-trending and east-vergent anticline ("Tierra Amarilla Anticlinorium"), which is related to the positive reactivation of a former Cretaceous normal fault (Elisa de Bordos Master Fault). Moreover, intercalations of high and low gravity anomalies and steep gravity gradients reveal a set of buried, west-tilted half-grabens associated with a synthetic normal fault pattern. These results, together with the uplift and folding style of the Cretaceous syn-rift recognized within the basin, suggest that their complete structural geometry could be explained by an inverted fault system linked to the shortening of pre-existing Cretaceous normal fault systems. Ages of the synorogenic deposits exposed unconformably over the frontal limb of the Tierra Amarilla Anticlinorium confirm a Late Cretaceous age for the Andean deformation and tectonic inversion of the basin.

  9. Exhumation of the Neuquén Basin in the southern Central Andes (Malargüe fold and thrust belt) from field data and low-temperature thermochronology

    NASA Astrophysics Data System (ADS)

    Folguera, A.; Bottesi, G.; Duddy, I.; Martín-González, F.; Orts, D.; Sagripanti, L.; Rojas Vera, E.; Ramos, V. A.

    2015-12-01

    Apatite fission-track analysis performed on eighteen Mesozoic sediment samples of the Neuquén Basin from the Southern Central Andes orogenic front between 35°30‧ and 37°S has revealed Campanian-Paleocene (75-55 Ma), late Eocene-early Oligocene (35-30 Ma) and middle Miocene (15-10 Ma) cooling episodes. Each cooling episode corresponds closely with major unconformities observed in the preserved sedimentary sequences, and is associated with kilometer-scale additional burial and subsequent exhumation. A similar degree of cooling is inferred from associated vitrinite reflectance data. Late Eocene-early Oligocene exhumation is recognized only near the eastern orogenic front adjacent to the foreland in the southernmost part of the study area and may be related partly to within-plate magmatism and associated extension in the Palaoco Basin. The Campanian-Paleocene and middle Miocene cooling episodes are recognized more widely in the fold and thrust belt and appear to coincide with periods of eastward arc expansion and mountain building processes.

  10. Plio-Quaternary thin-skinned tectonics along the crustal front flexure of the southern Central Andes: a record of the regional stress regime or of local tectonic-driven gravitational processes?

    NASA Astrophysics Data System (ADS)

    Messager, Grégoire; Nivière, Bertrand; Lacan, Pierre; Hervouët, Yves; Xavier, Jean-Paul

    2014-04-01

    We present here a record of Plio-Pleistocene deformations above the flexural front of the southern Central Andes of Argentina. We combine a seismic profile with structural and geomorphological observations to show that thin-skinned extension located on top of the crustal front flexure is coeval with thin-skinned shortening at the toe of the topographic bulge. The seismic line shows that a flat zone with no internal deformation separates the stretched and shortened domains. Such features are usually interpreted as the result of strike-slip faulting along basement faults, or tangential longitudinal strain folding in the soft sedimentary cover above crustal bending. We propose an alternative linking extension at the apex of the crustal anticline, to basal contraction by the downslope translation of a rigid thin nappe of sediments (30 × 30 km2 in area) above evaporites at a depth of 700-900 m. The size of such a process is unusually large onshore (630-810 km3) but mimics the gravity gliding observed in deltas and passive margins. Since this process disconnects zones with a shallow stress field from deeper crustal levels, it could allow extension above a compressive deformation front and should not be interpreted merely as a record of the crustal stress regime. Large-scale gravity gliding of the cover down the slope of a structural high could also explain some of the extension observed in mountain hinterlands.

  11. Glacial areas, lake areas, and snowlines from 1975 to 2012: status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    NASA Astrophysics Data System (ADS)

    Hanshaw, M. N.; Bookhagen, B.

    2013-02-01

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 144 multi-spectral satellite images spanning almost four decades, from 1975-2012, to obtain glacial and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. In a second step, we have estimated the snowline altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: first, since 1988 glacial areas throughout the Cordillera Vilcanota have been declining at a rate of 5.46 ± 1.70 km2 yr-1 (22-yr average, 1988-2010, with 95% confidence interval). The Quelccaya Ica Cap, specifically, has been declining at a rate of 0.67 ± 0.18 km2 yr-1 since 1980 (31-yr average, 1980-2011, also with 95% confidence interval); Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2011) as compared to the preceding decade (1990-2000); Third, the snowline of the Quelccaya Ice Cap is retreating to higher elevations as glacial areas decrease, by a total of almost 300 m between its lowest recorded elevation in 1989 and its highest in 1998; and fourth, as glacial regions have decreased, 61% of lakes connected to glacial watersheds have shown a roughly synchronous increase in lake area, while 84% of lakes not connected to glacial watersheds have remained stable or have declined in area. Our new and detailed data on glacial and lake areas over 37 yr provide an important spatiotemporal assessment of climate variability in this area. These data can be integrated into further studies

  12. Glacial areas, lake areas, and snow lines from 1975 to 2012: status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    NASA Astrophysics Data System (ADS)

    Hanshaw, M. N.; Bookhagen, B.

    2014-03-01

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 158 multi-spectral satellite images spanning almost 4 decades, from 1975 to 2012, to obtain glacial- and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. Additionally, we have estimated the snow-line altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: first, since 1988 glacial areas throughout the Cordillera Vilcanota (1988 glacial area: 361 km2) have been declining at a rate of 3.99 ± 1.15 km2 yr-1 (22 year average, 1988-2010, with 95% confidence interval (CI), n = 8 images). Since 1980, the Quelccaya Ice Cap (1980 glacial area: 63.1 km2) has been declining at a rate of 0.57 ± 0.10 km2 yr-1 (30 year average, 1980-2010, with 95% CI, n = 14). Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2010) as compared to the preceding decade (1988-1999) with an average increase from 37.5 to 42.3 × 10-3 km2 yr-1 km-2 (13%). Third, glaciers with lower median elevations are declining at higher rates than those with higher median elevations. Specifically, glaciers with median elevations around 5200 m a.s.l. are retreating to higher elevations at a rate of ~1 m yr-1 faster than glaciers with median elevations around 5400 m a.s.l. Fourth, as glacial regions have decreased, 77% of lakes connected to glacial watersheds have either remained stable or shown a roughly synchronous increase in lake area, while 42% of lakes not connected to glacial

  13. Glacial areas, lakes areas, and snowlines from 1975-2012: Status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    NASA Astrophysics Data System (ADS)

    Hanshaw, Maiana Natania

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 144 multi-spectral satellite images spanning almost four decades, from 1975-2012, to obtain glacial and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. In a second step, we have estimated the snowline altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: First, since 1988 glacial areas throughout the Cordillera Vilcanota have been declining at a rate of 5.46 +/- 1.70 km2/yr (22-year average, 1988-2010, with 95 % confidence interval). The Quelccaya Ica Cap, specifically, has been declining at a rate of 0.67 +/- 0.18 km2/yr since 1980 (31-year average, 1980-2011, also with 95 % confidence interval); Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2011) as compared to the preceding decade (1990-2000); Third, the snowline of the Quelccaya Ice Cap is retreating to higher elevations as glacial areas decrease, by a total of almost 300 m between its lowest recorded elevation in 1989 and its highest in 1998; and fourth, as glacial regions have decreased, 61 % of lakes connected to glacial watersheds have shown a roughly synchronous increase in lake area, while 84 % of lakes not connected to glacial watersheds have remained stable or have declined in area. Our new and detailed data on glacial and lake areas over 37 years provide an important spatiotemporal assessment of climate variability in this area. These data can be integrated into further

  14. Description and phylogeny of three new species of Synophis (Colubridae, Dipsadinae) from the tropical Andes in Ecuador and Peru

    PubMed Central

    Torres-Carvajal, Omar; Echevarría, Lourdes Y.; Venegas, Pablo J.; Germán Chávez; Camper, Jeffrey D.

    2015-01-01

    Abstract The discovery of three new species of Synophis snakes from the eastern slopes of the tropical Andes in Ecuador and Peru is reported. All previous records of Synophis bicolor from eastern Ecuador correspond to Synophis bogerti sp. n., which occurs between 1000–1750 m along a large part of the Amazonian slopes of the Ecuadorian Andes. In contrast, Synophis zamora sp. n. is restricted to southeastern Ecuador, including Cordillera del Cóndor, between 1543–1843 m. Synophis insulomontanus sp. n. is from the eastern slopes of the Andes in central and northern Peru, between 1122–1798 m, and represents the first record of Synophis from this country. All three new species share in common a large lateral spine at the base of the hemipenial body. A molecular phylogenetic tree based on three mitochondrial genes is presented, including samples of Diaphorolepis wagneri. Our tree strongly supports Synophis and Diaphorolepis as sister taxa, as well as monophyly of the three new species described here and Synophis calamitus. Inclusion of Synophis and Diaphorolepis within Dipsadinae as sister to a clade containing Imantodes, Dipsas, Ninia, Hypsiglena and Pseudoleptodeira is also supported. PMID:26798310

  15. Description and phylogeny of three new species of Synophis (Colubridae, Dipsadinae) from the tropical Andes in Ecuador and Peru.

    PubMed

    Torres-Carvajal, Omar; Echevarría, Lourdes Y; Venegas, Pablo J; Germán Chávez; Camper, Jeffrey D

    2015-01-01

    The discovery of three new species of Synophis snakes from the eastern slopes of the tropical Andes in Ecuador and Peru is reported. All previous records of Synophis bicolor from eastern Ecuador correspond to Synophis bogerti sp. n., which occurs between 1000-1750 m along a large part of the Amazonian slopes of the Ecuadorian Andes. In contrast, Synophis zamora sp. n. is restricted to southeastern Ecuador, including Cordillera del Cóndor, between 1543-1843 m. Synophis insulomontanus sp. n. is from the eastern slopes of the Andes in central and northern Peru, between 1122-1798 m, and represents the first record of Synophis from this country. All three new species share in common a large lateral spine at the base of the hemipenial body. A molecular phylogenetic tree based on three mitochondrial genes is presented, including samples of Diaphorolepis wagneri. Our tree strongly supports Synophis and Diaphorolepis as sister taxa, as well as monophyly of the three new species described here and Synophis calamitus. Inclusion of Synophis and Diaphorolepis within Dipsadinae as sister to a clade containing Imantodes, Dipsas, Ninia, Hypsiglena and Pseudoleptodeira is also supported.

  16. Description and phylogeny of three new species of Synophis (Colubridae, Dipsadinae) from the tropical Andes in Ecuador and Peru.

    PubMed

    Torres-Carvajal, Omar; Echevarría, Lourdes Y; Venegas, Pablo J; Germán Chávez; Camper, Jeffrey D

    2015-01-01

    The discovery of three new species of Synophis snakes from the eastern slopes of the tropical Andes in Ecuador and Peru is reported. All previous records of Synophis bicolor from eastern Ecuador correspond to Synophis bogerti sp. n., which occurs between 1000-1750 m along a large part of the Amazonian slopes of the Ecuadorian Andes. In contrast, Synophis zamora sp. n. is restricted to southeastern Ecuador, including Cordillera del Cóndor, between 1543-1843 m. Synophis insulomontanus sp. n. is from the eastern slopes of the Andes in central and northern Peru, between 1122-1798 m, and represents the first record of Synophis from this country. All three new species share in common a large lateral spine at the base of the hemipenial body. A molecular phylogenetic tree based on three mitochondrial genes is presented, including samples of Diaphorolepis wagneri. Our tree strongly supports Synophis and Diaphorolepis as sister taxa, as well as monophyly of the three new species described here and Synophis calamitus. Inclusion of Synophis and Diaphorolepis within Dipsadinae as sister to a clade containing Imantodes, Dipsas, Ninia, Hypsiglena and Pseudoleptodeira is also supported. PMID:26798310

  17. Instantánea de los cánceres de cerebro y del sistema nervioso central

    Cancer.gov

    Información sobre las tendencias de incidencia, mortalidad y financiamiento del NCI sobre los cánceres de cerebro y del sistema nervioso central; así como ejemplos de actividades del NCI y adelantos en la investigación de estos tipos de cáncer.

  18. Quarterly progress report for Concilio Central - Agua Caliente Del Sol

    SciTech Connect

    Berg, E.

    1982-01-21

    The Concilio Central has completed the five (5) solar water heaters called for in the project. In total the project was a learning experience for all involved and did demonstrate the validity of using the sun's energy to heat water for residential use. Each of the five heaters constructed and installed produce sixty-six (66) gallons of 110/sup 0/ water (average temperature) every sunny day. The residents who received the water heaters are satisfied with the water temperature and amount and readily adapted to the availability of hot water in their homes.

  19. Combining point and distributed snowpack data with landscape-based discretization for hydrologic modeling of the snow-dominated Maipo River Basin, in the semi-arid Andes central Chile

    NASA Astrophysics Data System (ADS)

    Videla Giering, Y. A., III; McPhee, J. P.

    2015-12-01

    Snow hydrology in mountain environments plays an important role in the availability of hydrological resources in warm climate areas and height effects, since the magnitude of snowpack, its spatial and temporal distribution is very important to determine the availability of water in the snowmelt season and take forward different productive activities This investigation models and assess the main phenomena hydrological cycle of snow using the software Cold Region Hydrological Model (Pomeroy et al., 2007). The software is a physically based model developed by the centre for hydrology, University of Saskatchewan. The aim of this model is to have a better understanding of hydrological processes involved in cold environments, which are particular in the sense that a host of specific phenomena such as snow and ice accumulation, transport and melt, infiltration through frozen soils, and the like, control the hydrograph timing) The analysis involved the development of a hydrologic model for the Upper Maipo River Basin, with elevations between 800 and 6500 meters above sea level and 5000-km^2 watershed in the Andes of Central Chile which supplies water resources to the capital city of Santiago (7 million inhabitants), to a thriving agricultural region, as well as to hydropower and large mining activities. The paper concludes that there is a differential distribution of snow cover in the study area, determined mainly by steep terrain geomorphology. These factors have been considered in the parameterization of the model, showing considerable variation in storage time, redistributions by blowing snow, melting intervals, infiltration rates and drainage basin. The fictional scenarios modeled demonstrate noticeable changes in the hydrograph, showing the fragile climate and hydrological condition of this basin of Central Chile.

  20. The Amazon-Laurentian connection as viewed from the Middle Proterozoic rocks in the central Andes, western Bolivia and northern Chile

    USGS Publications Warehouse

    Tosdal, R.M.

    1996-01-01

    Middle Proterozoic rocks underlying the Andes in western Bolivia, western Argentina, and northern Chile and Early Proterozoic rocks of the Arequipa massif in southern Peru?? from the Arequipa-Antofalla craton. These rocks are discontinuously exposed beneath Mesozoic and Cenozoic rocks, but abundant crystalline clasts in Tertiary sedimentary rocks in the western altiplano allow indirect samples of the craton. Near Berenguela, western Bolivia, the Oligocene and Miocene Mauri Formation contains boulders of granodiorite augen gneiss (1171??20 Ma and 1158??12 Ma; U-Pb zircon), quartzose gneiss and granofels that are inferred to have arkosic protoliths (1100 Ma source region; U-Pb zircon), quartzofeldspathic and mafic orthogneisses that have amphibolite- and granulite-facies metamorphic mineral assemblages (???1080 Ma metamorphism; U-Pb zircon), and undeformed granitic rocks of Phanerozoic(?) age. The Middle Proterozoic crystalline rocks from Berenguela and elsewhere in western Bolivia and from the Middle Proterozoic Bele??n Schist in northern Chile generally have present-day low 206Pb/204Pb ( 15.57), and elevated 208Pb/204Pb (37.2 to 50.7) indicative of high time-averaged Th/U values. The Middle Proterozoic rocks in general have higher presentday 206Pb/204Pb values than those of the Early Proterozoic rocks of the Arequipa massif (206Pb/204Pb between 16.1 and 17.1) but lower than rocks of the southern Arequipa-Antofalla craton (206Pb/204Pb> 18.5), a difference inferred to reflect Grenvillian granulite metamorphism. The Pb isotopic compositions for the various Proterozoic rocks lie on common Pb isotopic growth curves, implying that Pb incorporated in rocks composing the Arequipa-Antofalla craton was extracted from a similar evolving Pb isotopic reservoir. Evidently, the craton has been a coherent terrane since the Middle Proterozoic. Moreover, the Pb isotopic compositions for the Arequipa-Antofalla craton overlap those of the Amazon craton, thereby supporting a link

  1. A tectonically controlled basin-fill within the Valle del Cauca, West-Central Colombia

    SciTech Connect

    Rine, J.M.; Keith, J.F. Jr.; Alfonso, C.A.; Ballesteros, I.; Laverde, F.; Sacks, P.E.; Secor, D.T. Jr. ); Perez, V.E.; Bernal, I.; Cordoba, F.; Numpaque, L.E. )

    1993-02-01

    Tertiary strata of the Valle del Cauca reflect a forearc/foreland basin tectonic history spanning a period from pre-uplift of the Cordillera Central to initiation of uplift of the Cordillera Occidental. Stratigraphy of the Valle del Cauca begins with Jurassic-Cretaceous rocks of exotic and/or volcanic provenance and of oceanic origin. Unconformably overlying these are Eocene to Oligocene basal quartz-rich sandstones, shallow marine algal limestones, and fine-grained fluvial/deltaic mudstones and sandstones with coalbeds. These Eocene to Oligocene deposits represent a period of low tectonic activity. During late Oligocene to early Miocene, increased tectonic activity produced conglomeratic sediments which were transported from east to west, apparently derived from uplift of the Cordillera Central, and deposited within a fluvial to deltaic setting. East-west shortening of the Valle del Cauca basin folded the Eocene to early Miocene units, and additional uplift of the Cordillera Central during the later Miocene resulted in syn-tectonic deposition of alluvial fans. After additional fold and thrust deformation of the total Eocene-Miocene basin-fill, tectonic activity abated and Pliocene-Quaternary alluvial and lacustrine strata were deposited. Within the framework of this depositional and tectonic history of the Valle del Cauca, hydrocarbon exploration strategies can be formulated and evaluated.

  2. Diversity of extremophilic bacteria in the sediment of high-altitude lakes located in the mountain desert of Ojos del Salado volcano, Dry-Andes.

    PubMed

    Aszalós, Júlia Margit; Krett, Gergely; Anda, Dóra; Márialigeti, Károly; Nagy, Balázs; Borsodi, Andrea K

    2016-09-01

    Ojos del Salado, the highest volcano on Earth is surrounded by a special mountain desert with extreme aridity, great daily temperature range, intense solar radiation, and permafrost from 5000 meters above sea level. Several saline lakes and permafrost derived high-altitude lakes can be found in this area, often surrounded by fumaroles and hot springs. The aim of this study was to gain information about the bacterial communities inhabiting the sediment of high-altitude lakes of the Ojos del Salado region located between 3770 and 6500 m. Altogether 11 sediment samples from 4 different altitudes were examined with 16S rRNA gene based denaturing gradient gel electrophoresis and clone libraries. Members of 17 phyla or candidate divisions were detected with the dominance of Proteobacteria, Acidobacteria, Actinobacteria and Bacteroidetes. The bacterial community composition was determined mainly by the altitude of the sampling sites; nevertheless, the extreme aridity and the active volcanism had a strong influence on it. Most of the sequences showed the highest relation to bacterial species or uncultured clones from similar extreme environments. PMID:27315168

  3. Diversity of extremophilic bacteria in the sediment of high-altitude lakes located in the mountain desert of Ojos del Salado volcano, Dry-Andes.

    PubMed

    Aszalós, Júlia Margit; Krett, Gergely; Anda, Dóra; Márialigeti, Károly; Nagy, Balázs; Borsodi, Andrea K

    2016-09-01

    Ojos del Salado, the highest volcano on Earth is surrounded by a special mountain desert with extreme aridity, great daily temperature range, intense solar radiation, and permafrost from 5000 meters above sea level. Several saline lakes and permafrost derived high-altitude lakes can be found in this area, often surrounded by fumaroles and hot springs. The aim of this study was to gain information about the bacterial communities inhabiting the sediment of high-altitude lakes of the Ojos del Salado region located between 3770 and 6500 m. Altogether 11 sediment samples from 4 different altitudes were examined with 16S rRNA gene based denaturing gradient gel electrophoresis and clone libraries. Members of 17 phyla or candidate divisions were detected with the dominance of Proteobacteria, Acidobacteria, Actinobacteria and Bacteroidetes. The bacterial community composition was determined mainly by the altitude of the sampling sites; nevertheless, the extreme aridity and the active volcanism had a strong influence on it. Most of the sequences showed the highest relation to bacterial species or uncultured clones from similar extreme environments.

  4. Field study and three-dimensional reconstruction of thrusts and strike-slip faults in the Central Andes: implications for deep-seated geothermal circulation and ore deposits exploration

    NASA Astrophysics Data System (ADS)

    Norini, Gianluca; Groppelli, Gianluca; Giordano, Guido; Baez, Walter; Becchio, Raul; Viramonte, Jose; Arnosio, Marcelo

    2014-05-01

    The Puna plateau (NW Argentina), located in the back-arc of the Central Andes, is a plateau characterized by both orogen-parallel and orogen-oblique deformation styles, extensive magmatic and geothermal activity, and the broad occurrence of igneous and hydrothermal ore-forming minerals. In this area, like in other convergent margins, the behaviour of the magma-tectonics interplay can affect the circulation of hydrothermal fluids, so that the full comprehension of the tectonic control on the magmas and fluids paths in the continental crust is crucial to plan the geothermal and ore exploration. In this study, we present a structural analysis of the back-arc portion of the orogen-oblique Calama-Olacapato-El Toro fault system and the surrounding orogen-parallel thrust faults in the central-eastern Puna Plateau, comprising the Cerro Tuzgle-Tocomar geothermal volcanic area, with high geothermal potential, and silicic calderas and domes associated with epithermal ore deposits. We also focused on the tectonic and volcanotectonic structures of the Chimpa and Tuzgle stratovolcanoes, two of the most important polygenetic volcanic centres of the plateau. Morphostructural analysis and field mapping reveal the geometry, kinematics and dynamics of the tectonic structures of the studied area. These data and the available stratigraphic and geophysical data have been integrated with the software MOVE and PETREL in a three-dimensional reconstruction of the main fault planes, showing their attitude and intersections at depth. As a result of our study, we show that despite different geometry and kinematics of the Calama-Olacapato-El Toro fault system and the thrust faults, they formed and evolved under the same progressive evolving dynamic state, forming a single tectonic system and accommodating crustal shortening of a thickened crust. In this frame, the crust underwent simultaneous deformation along both the low-angle thrust faults and the vertical transcurrent strike-slip faults

  5. PAH fluxes in the Laja Lake of south central Chile Andes over the last 50 years: evidence from a dated sediment core.

    PubMed

    Quiroz, Roberto; Popp, Peter; Urrutia, Roberto; Bauer, Coretta; Araneda, Alberto; Treutler, Hanns-Christian; Barra, Ricardo

    2005-10-15

    This paper reports the occurrence of polyaromatic hydrocarbons (PAHs) deposition inferred from a sediment core of an Andean lake in south central Chile. Sediments were carefully collected from one of the deepest section of the lake and sliced every 1 cm. The samples were analyzed for PAHs, (137)Cs, (210)Pb, organic carbon and grain-size. The stratigraphic chronology and the sedimentation rates were estimated using the sedimentary signature left by the (137)Cs and (210)Pb fallout as temporal markers. PAHs were quantified by HPLC-fluorescence detection (HPLC-Fluorescence). 15 priority EPA PAHs were analyzed in this study. Based on these results, PAH deposition over the last 50 years was estimated (a period characterized by an important intervention in the area). PAH concentration ranged from 226 to 620 ng g(-1) d.w. The highest concentrations of PAHs were found in the core's bottom. The PAH profile is dominated by the presence of perylene indicating a natural source of PAH. In addition, two clear PAH deposition periods could be determined: the most recent with two-four rings PAHs, the older one with five-seven rings predomination. Determined fluxes where 71 to 972 microg m(-2) year(-1), dominated by perylene deposition. PAH levels and fluxes are lower compared to the levels found in sediments from remote lakes in Europe and North America. It is concluded that the main source of PAHs into the Laja Lake sediments are of natural origin.

  6. 78 FR 24228 - Lake Andes National Wildlife Refuge Complex, Lake Andes, SD; Final Comprehensive Conservation Plan

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-04-24

    ... review and comment following the announcement in the Federal Register on October 29, 2012 ] (77 FR 65574... Fish and Wildlife Service Lake Andes National Wildlife Refuge Complex, Lake Andes, SD; Final... Complex (Complex), which includes Lake Andes NWR, Karl E. Mundt NWR, and Lake Andes Wetland...

  7. 77 FR 65574 - Lake Andes National Wildlife Refuge Complex, Lake Andes, SD; Draft Comprehensive Conservation...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-29

    ... Complex. We started this process through a notice in the Federal Register (72 FR 27328; May, 15, 2007... Fish and Wildlife Service Lake Andes National Wildlife Refuge Complex, Lake Andes, SD; Draft... assessment (EA) for the Lake Andes National Wildlife Refuge Complex (Complex), which includes Lake Andes...

  8. Active and passive seismic imaging of the Precordilleran crust, fore-arc of the North-Chilean subduction zone (Central Andes)

    NASA Astrophysics Data System (ADS)

    Wenske, Ina; Hellwig, Olaf; Buske, Stefan; Wigger, Peter; Shapiro, Serge A.

    2014-05-01

    In the fore-arc of the Chilean subduction zone the prominent trench-parallel fault systems can be traced for several thousand kilometers in the north-south direction. These fault systems possibly crosscut parts or the entire crust and are expected to have a close relationship to transient processes of the subduction earthquake cycle. With the motivation to image and characterize the structural inventory and the processes that occur in the vicinity of these large-scale fault zones, we are currently performing a combined analysis of active and passive seismic data sets. The active-seismic data analysis is intended to provide images of the faults at depth and allow linking surface information to subsurface structures. The correlation of the active seismic data with the observed seismicity around these fault systems complements the image and potentially reveals the origin and the nature of the seismicity (including tremors) bound to these fault systems. In 1996, an approximately 350 km long, west-east running reflection seismic profile was acquired to image the entire crust of the Central Andean fore-arc system (North Chile; ANCORP96 seismic line). Several features such as the downgoing plate (Nazca reflector) and the Quebrada Blanca Bright Spot at mid-crustal level were clearly imaged using both standard CMP processing and Kirchhoff prestack depth migration. The latter proved to be more successful in coping with the low data coverage and varying data quality. However, the original images did not provide conclusive information on the upper crust (< 10 km depth) due to the sparse acquisition geom- etry and the insufficient removal of source-generated noise. The major goal of our current re-processing of the ANCORP96 reflection seismic data set is to provide improved images of the upper and middle crust, Thereby, resolving the shallow and perhaps steeply dipping segments of the major fault systems, which were not detected by the original processing. This is done by using

  9. Spatial diversity patterns of Pristimantis frogs in the Tropical Andes.

    PubMed

    Meza-Joya, Fabio Leonardo; Torres, Mauricio

    2016-04-01

    Although biodiversity gradients have been widely documented, the factors governing broad-scale patterns in species richness are still a source of intense debate and interest in ecology, evolution, and conservation biology. Here, we tested whether spatial hypotheses (species-area effect, topographic heterogeneity, mid-domain null model, and latitudinal effect) explain the pattern of diversity observed along the altitudinal gradient of Andean rain frogs of the genus Pristimantis. We compiled a gamma-diversity database of 378 species of Pristimantis from the tropical Andes, specifically from Colombia to Bolivia, using records collected above 500 m.a.s.l. Analyses were performed at three spatial levels: Tropical Andes as a whole, split in its two main domains (Northern and Central Andes), and split in its 11 main mountain ranges. Species richness, area, and topographic heterogeneity were calculated for each 500-m-width elevational band. Spatial hypotheses were tested using linear regression models. We examined the fit of the observed diversity to the mid-domain hypothesis using randomizations. The species richness of Pristimantis showed a hump-shaped pattern across most of the altitudinal gradients of the Tropical Andes. There was high variability in the relationship between area and species richness along the Tropical Andes. Correcting for area effects had little impact in the shape of the empirical pattern of biodiversity curves. Mid-domain models produced similar gradients in species richness relative to empirical gradients, but the fit varied among mountain ranges. The effect of topographic heterogeneity on species richness varied among mountain ranges. There was a significant negative relationship between latitude and species richness. Our findings suggest that spatial processes partially explain the richness patterns of Pristimantis frogs along the Tropical Andes. Explaining the current patterns of biodiversity in this hot spot may require further studies on

  10. Active seismic and microseismic reflection imaging of the Precordilleran crust, fore-arc of the North-Chilean subduction zone (Central Andes)

    NASA Astrophysics Data System (ADS)

    Wenske, Ina; Hellwig, Olaf; Schmelzbach, Cedric; Buske, Stefan; Kummerow, Jörn; Wigger, Peter; Shapiro, Serge A.

    2013-04-01

    In the fore-arc of the Chilean subduction zone, prominent trench-parallel fault systems can be traced for more than thousand kilometers in north-south direction. These fault systems possibly crosscut parts or the entire crust and are expected to have a close relationship to transient processes of the subduction earthquake cycle. With the motivation to image and characterize the structural inventory and the processes that occur in the vicinity of these large-scale fault zones, we are currently performing a combined analysis of active and passive seismic data sets. The active-seismic data analysis is intended to provide images of the faults at depth and allow linking surface information to subsurface structures. The correlation of the active seismic data with the observed seismicity around these fault systems complements the imaging and potentially reveals the origin and the nature of the seismicity (incl. tremors) bound to these fault systems. Furthermore, reflection information extracted from passive-seismic waveform data has the potential to complement the active seismic imaging. In 1996, an approximately 350 km long west-east running reflection seismic profile was acquired to image the entire crust of the Central Andean fore-arc system (North Chile; ANCORP96 seismic line). Several features such as the downgoing plate (Nazca reflector) and the Quebrada Blanca Bright Spot at mid-crustal level were clearly imaged using both standard CMP processing and Kirchhoff prestack depth migration. The latter proved to be more successful in coping with the low data coverage and varying data quality. However, the original images were not providing conclusive information on the upper crust (< 10 km depth) due to the sparse acquisition geometry and the partly insufficient removal of source-generated noise. The major goal of our current re-processing of the ANCORP96 reflection seismic data set using adapted noise-suppression schemes and a novel prestack depth migration technique

  11. A Precambrian cratonic block in the west-central Chihuahua - The Sierra del Nido cratonic block

    SciTech Connect

    Goodell, P.C. . Dept. of Geological)

    1993-02-01

    Precambrian rocks in west-central Chihuahua have been recognized by Denison (1969) and Mauger et al. (1983), on the basis of radiometric dating. The rocks are rhyolite clasts, and an allucthonous block, respectively, however their source direction and vergence can be measured. They point back to and are on the edge of a large, uniform, negative Bouguer gravity anomaly, having values greater than 200 milligals. The isotopic geochemical character of several Tertiary felsic fields within this anomalous are has been determined, and initial strontium isotopic ratios are all greater than 0.7055. Outside the anomalous area these ratios are lower, and Basin and Range extension tectonism is more evident. It is proposed that a Precambrian cratonic block, the Sierra del Nido, is present in the crust in west-central Chihuahua. It is reasonable to propose that it was decreted from North America during a Precambrian extensional (1.1. By ) event, from somewhere along the Arizona Transition Zone-Texas Linament region. The Sierra del Nido Block is separated form the ATZ-TL by a region of disrupted craton and extended crust, the Basin and Range Province. Implications of the pressure of the Sierra del Nido Block on other regional tectonic events will be discussed.

  12. Structure and tectonic evolution of the Fuegian Andes (southernmost South America) in the framework of the Scotia Arc development

    NASA Astrophysics Data System (ADS)

    Torres Carbonell, Pablo J.; Dimieri, Luis V.; Olivero, Eduardo B.; Bohoyo, Fernando; Galindo-Zaldívar, Jesús

    2014-12-01

    The major structural and tectonic features of the Fuegian Andes provide an outstanding onshore geological framework that aids in the understanding of the tectonic evolution of the Scotia Arc, mainly known from offshore studies. The orogenic history of the Fuegian Andes (Late Cretaceous-Miocene) is thus compared and integrated with the tectonic history of the Scotia Sea. Late Cretaceous-Paleocene structures in the Fuegian Andes suggest a N-directed contraction consistent with an oroclinal bending of the southernmost South America-Antarctic Peninsula continental bridge. This N-directed contraction in the Fuegian Andes continued during the spreading of the West Scotia Ridge, between 40-50 and 10 Ma ago. The onset of major strike-slip faulting in Tierra del Fuego is considered here to be not older than the late Miocene, consistent with the recent history of the North Scotia Ridge; thus forming part of a tectonic regime superposed to the prior contraction in the Fuegian Andes.

  13. Mountain building processes in the Central Andes

    NASA Technical Reports Server (NTRS)

    Bloom, A. L.; Isacks, B. L.

    1986-01-01

    False color composite images of the Thematic Mapper (TM) bands 5, 4, and 2 were examined to make visual interpretations of geological features. The use of the roam mode of image display with the International Imaging Systems (IIS) System 600 image processing package running on the IIS Model 75 was very useful. Several areas in which good comparisons with ground data existed, were examined in detail. Parallel to the visual approach, image processing methods are being developed which allow the complete use of the seven TM bands. The data was organized into easily accessible files and a visual cataloging of the quads (quarter TM scenes) with preliminary registration with the best available charts for the region. The catalog has proved to be a valuable tool for the rapid scanning of quads for a specific investigation. Integration of the data into a complete approach to the problems of uplift, deformation, and magnetism in relation to the Nazca-South American plate interaction is at an initial stage.

  14. Charles Darwin in the Andes

    ERIC Educational Resources Information Center

    Bizzo, Nelio; Bizzo, Luis Eduardo Maestrelli

    2006-01-01

    Considering geological time as an important epistemological obstacle to the construction of ideas on biological evolution, a study was carried out on the so-called "Darwin Papers". The conclusion was that Charles Darwin's excursion in the Andes during March-April 1835 was a crucial step in this regard. An expedition was carried out in March-April…

  15. Lithospheric scale model of Merida Andes, Venezuela (GIAME Project)

    NASA Astrophysics Data System (ADS)

    Schmitz, M.; Orihuela, N. D.; Klarica, S.; Gil, E.; Levander, A.; Audemard, F. A.; Mazuera, F.; Avila, J.

    2013-05-01

    Merida Andes (MA) is one of the most important orogenic belt in Venezuela and represents the northern culmination of South America Andes. During the last 60 years, several models have been proposed to explain the shallow and deep structure, using different geological, geophysical, seismological, geochemical and petrologic concepts; nevertheless, most of them have applied local observation windows, and do not represent the major structure of MA. Therefore, a multidisciplinary research group, coordinated by FUNVISIS, in close cooperation with UCV, ULA and PDVSA, is proposed in order to get the outlined goals in the project entitled GIAME ("Geociencia Integral de los Andes de MErida") was established, which aims to generate a lithospheric scale model and the development of a temporal dynamic model for the MA. As a base for lithospheric investigations of the Merida Andes, we are proposing three wide angle seismic profiles across the orogen on three representative sites, in order to determine the inner structure and its relation with the orogen's gravimetric root. To the date, there are no seismic studies at lithospheric scale which cross MA. The wide angle seismic will be complemented with the re-processing and re-interpretation of existing reflection seismic data, which will allow to establish a relationship between MA and its associated flexural basins (Maracaibo and Barinas-Apure basins). Depending on the results of the VENCORP Project (VENezuelan COntinental Reflection Profiling), which might show some reliable results about crustal features and Moho reflectors along three long seismic profiles at Caribbean Moutain system, a reflection seismic profile across the central portion of MA is proposed. Additional tasks, consisting in MA quaternary deformation studies, using research methods like neotectonics and paleoseismology, georadar, numerical modeling, cinematic GPS, SAR interferometry, thermocronology, detailed studies on regional geology, flexural modeling

  16. Epochs of intrusion-related copper mineralization in the Andes

    NASA Astrophysics Data System (ADS)

    Sillitoe, R. H.

    Seventy-four copper deposits and prospects related intimately to intrusive activity in the Andes have been dated radiometrically during the last 18 years by many different investigators, most of whom used the KAr method. The results are summarized and some of their local and regional implications are reviewed. A number of copper deposits, mainly of the porphyry type, were emplaced in, or near to, premineral volcanic sequences and (or) equigranular plutons. Such precursor volcanism lasted for as long as 9 Ma, and preceded mineralization by intervals of from less than 1 Ma to as much as 9 Ma. Precursor plutons were emplaced no more than 2 to 3 Ma prior to mineralization at several localities in Chile, but possibly as long as 10 to 30 Ma earlier in parts of Colombia and Peru. The time separating emplacement of progenitor stocks and hydrothermal alteration and accompanying copper mineralization, and the duration of alteration-mineralization sequences generally are both less than the analytical uncertainty of the KAr method. However, on the basis of a detailed study of the Julcani vein system in Peru and less clearcut evidence from elsewhere, it may be concluded that alteration and copper mineralization followed stock or dome emplacement by substantially less than 1 Ma and lasted for 0.5 to 2 Ma and, locally, possibly as long as 3 Ma. At several localities, post-mineral magmatic activity could not be separated by the KAr method from the preceding alteration-mineralization events. As many as nine epochs of copper mineralization, ranging in age from late Paleozoic to late Pliocene-Pleistocene, are recognizable in the central Andes of Chile, Peru, Bolivia, and Argentina, and at least four somewhat different epochs characterize the northern Andes of Colombia. Each epoch coincides with a discrete linear sub-belt, some of which extend for more than 2000 km along the length of the orogen. More than 90% of Andean copper resources, mainly as porphyry deposits, are

  17. Stepwise colonization of the Andes by ruddy ducks and the evolution of novel β-globin variants.

    PubMed

    Muñoz-Fuentes, V; Cortázar-Chinarro, M; Lozano-Jaramillo, M; McCracken, K G

    2013-03-01

    Andean uplift played a key role in Neotropical bird diversification, yet past dispersal and genetic adaptation to high-altitude environments remain little understood. Here we use multilocus population genetics to study population history and historical demographic processes in the ruddy duck (Oxyura jamaicensis), a stiff-tailed diving duck comprising three subspecies distributed from Canada to Tierra del Fuego and inhabiting wetlands from sea level to 4500 m in the Andes. We sequenced the mitochondrial DNA, four autosomal introns and three haemoglobin genes (α(A), α(D), β(A)) and used isolation-with-migration (IM) models to study gene flow between North America and South America, and between the tropical and southern Andes. Our analyses indicated that ruddy ducks dispersed first from North America to the tropical Andes, then from the tropical Andes to the southern Andes. While no nonsynonymous substitutions were found in either α globin gene, three amino acid substitutions were observed in the β(A) globin. Based on phylogenetic reconstruction and power analysis, the first β(A) substitution, found in all Andean individuals, was acquired when ruddy ducks dispersed from low altitude in North America to high altitude in the tropical Andes, whereas the two additional substitutions occurred more recently, when ruddy ducks dispersed from high altitude in the tropical Andes to low altitude in the southern Andes. This stepwise colonization pattern accompanied by polarized β(A) globin amino acid replacements suggest that ruddy ducks first acclimatized or adapted to the Andean highlands and then again to the lowlands. In addition, ruddy ducks colonized the Andean highlands via a less common route as compared to other waterbird species that colonized the Andes northwards from the southern cone of South America. PMID:23346994

  18. Late Cenozoic Exhumation in the Northern Peruvian Andes

    NASA Astrophysics Data System (ADS)

    Michalak, M.; Hall, S. R.; Farber, D.; Hourigan, J. K.

    2011-12-01

    Orogens represent first-order morphological manifestations of the dynamical forces that drive plate tectonics. Despite advances in techniques that quantify geologic processes, understanding these processes at a continental scale remains challenging. The South American Andes are an example of a long-lived, morphologically and tectonically segmented orogen. The Northern Peruvian Andes are characterized by flat slab subduction and a relatively narrow section of high topography, in contrast to the central Andes, which contain the broad Altiplano-Puna plateau and normal-angle subduction. Current models of Andean orogenesis suggest that most of the high topography evolved recently beginning about 10-20Ma. Recent data from the Central Andes further suggest that this uplift occurred rapidly from ~6-10Ma. However, as many of these data are from the central Andean region, they may not be directly applicable to the entire Andean chain. Therefore, it is critical to investigate areas outside of the central Andean region using similar techniques to test the applicability of these models elsewhere in the Andes. Here, we use low-temperature thermochronology to characterize the shallow crustal cooling history from four sites in the northern Peruvian Andes, across three degrees of latitude (5°S to 8°S). By using both apatite and zircon (U-Th)/He thermochronometers we are able to record rates of crustal exhumation as well as temporal and spatial accelerations and decelerations of exhumation. In contrast to previous studies based on stratigraphical, structural and sedimentological relationships, our preliminary results show no significant exhumation until the Miocene in the Eastern Cordillera of Northern Peru. In general, our results indicate slow exhumation (<0.01 mm/yr) during the Mesozoic and early Cenozoic and record an acceleration of exhumation in the late Miocene to the present, to rates of 0.2-0.5 mm/yr. This regional acceleration signal occurs in field sites in the north (5

  19. Sediment yield along the Andes: continental budget, regional variations, and comparisons with other basins from orogenic mountain belts

    NASA Astrophysics Data System (ADS)

    Latrubesse, Edgardo M.; Restrepo, Juan D.

    2014-07-01

    We assess the sediment yield at 119 gauging stations distributed from Colombia to Patagonia, covering the different morphotectonic and morphoclimatic settings of the Andes. The most productive areas are the Meta River basin within the northern Andes and the Bolivian and northern Argentina-Chaco systems, which produce an average of 3345, 4909 and 2654 t km2 y- 1 of sediment, respectively. The rivers of the northern and central Andes (excluding the Pacific watersheds of Peru, northern Chile, and central Argentina) have a weighted mean sediment yield of 2045 t km- 2 y- 1 and produce 2.25 GTy- 1 of total sediment. A major constraint estimating the Andean continental budget of sediment yield lies in the lack of gauging data for the Peruvian region. Using the available gauge stations, the regional sediment yield appears underestimated. Assuming a higher value of sediment yield for the Peruvian Andes, the total budget for the whole central Andes could range between 2.57 GT y- 1 and 3.44 GT y- 1. A minimum of ~ 0.55 GT y- 1 and a probable maximum of ~ 1.74 GT y- 1 of sediment are deposited in the intramontane and surrounding proximal sedimentary basins. The magnitude of sediment yield in the Andes is comparable to other rivers draining orogenic belts around the world.

  20. Western Slope of Andes, Peru

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Along the western flank of the Andes, 400 km SE of Lima Peru, erosion has carved the mountain slopes into long, narrow serpentine ridges. The gently-sloping sediments have been turned into a plate of worms wiggling their way downhill to the ocean.

    The image was acquired September 28, 2004, covers an area of 38 x 31.6 km, and is located near 14.7 degrees south latitude, 74.5 degrees west longitude.

    The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

  1. Evolution of the east-central San Jose del Cabo basin, Baja California Sur, Mexico

    NASA Astrophysics Data System (ADS)

    McTeague, M. S.; Umhoefer, P. J.; Schwennicke, T.; Ingle, J. C.; Cortes Martinez, M.

    2006-12-01

    The San Jose del Cabo basin at the southern tip of the Baja California peninsula records the early tectonic evolution of the west side of the Gulf of California. This study focused on the east central margin of the basin. The basal La Calera Formation unconformably overlies Cretaceous granite and consists of conglomerate, pebbly sandstone and conglomerate, and sandstone deposited in alluvial fans and fan-deltas. Deposition of the La Calera Formation was from ca. 9-14 Ma. The lower member of the Trinidad Formation was deposited beginning ca. 9-13 Ma and consists of sandstone, mudstone, and shelly mudstone deposited in nearshore and estuarine environments. These age estimates are based on sedimentation rates and foraminifera and coccoliths from the NN 11A nannozone (7.4 8.6 Ma, GTS 2004). The middle member of the Trinidad Formation consists of deeper water mudstones deposited by turbidity currents and suspension settling in a shelf to slope and conglomerates deposited by submarine debris flows on the shelf. The basin began earlier than previously thought. The oldest marine rocks are ca.9-13 Ma, while sedimentation on the east side began at ca. 9-14 Ma, synchronous with estimates of initiation of offset on the San Jose del Cabo fault. The Zapote fault is a down-to-the-east normal and sinistral-oblique fault that exposes a wedge of granite and older strata in the footwall to the west. The fault was active during sedimentation in the late Miocene and possibly later. The fault divides the study area into an eastern hanging wall subbasin and western footwall subbasin. The eastern subbasin formed an embayment in the eastern margin of the Cabo basin. A regional flooding surface (ca. 8 Ma) can be correlated across the fault that marks a major marine incursion. Depositional systems evolved rapidly from coarse-grained terrestrial systems to fine-grained marine and estuarine systems. The Cabo basin provides an excellent analogue for comparison with offshore basins, which are

  2. Neotectonics in the foothills of the southernmost central Andes (37°-38°S): Evidence of strike-slip displacement along the Antiñir-Copahue fault zone

    NASA Astrophysics Data System (ADS)

    Folguera, AndréS.; Ramos, VíCtor A.; Hermanns, Reginald L.; Naranjo, José

    2004-10-01

    The Antiñir-Copahue fault zone (ACFZ) is the eastern orogenic front of the Andes between 38° and 37°S. It is formed by an east vergent fan of high-angle dextral transpressive and transtensive faults, which invert a Paleogene intra-arc rift system in an out of sequence order with respect to the Cretaceous to Miocene fold and thrust belt. 3.1-1.7 Ma volcanic rocks are folded and fractured through this belt, and recent indicators of fault activity in unconsolidated deposits suggest an ongoing deformation. In spite of the absence of substantial shallow seismicity associated with the orogenic front, neotectonic studies show the existence of active faults in the present mountain front. The low shallow seismicity could be linked to the high volumes of retroarc-derived volcanic rocks erupted through this fault system during Pliocene and Quaternary times. This thermally weakened basement accommodates the strain of the Antiñir-Copahue fault zone, absorbing the present convergence between the South America and Nazca plates.

  3. A review of the geology of the Argentinian Fuegian Andes

    NASA Astrophysics Data System (ADS)

    Olivero, Eduardo B.; Martinioni, Daniel R.

    2001-06-01

    Seven stratigraphic units reflect the tectonic evolution of the Argentinian Fuegian Andes: Basement (Paleozoic-Jurassic); Lemaire Formation (Upper Jurassic); Yahgan-Beauvoir formations (Lower Cretaceous); Cerro Matrero Formation (Upper Cretaceous); Rı´o Claro Formation (Paleocene); La Despedida Group (Eocene); and Cabo Peña Formation (uppermost Eocene-Lower Oligocene). Basement rocks (garnet, quartz-sericite, and chlorite schists; and amphibolites) are unconformably covered by the Lemaire Formation (rhyolites; basalts; slates; and acidic volcaniclastic breccias, tuffs, conglomerates, and turbidites), formed during extensional tectonism. The post-rift Yahgan Formation (deep-marine black mudstones, andesitic volcaniclastic turbidites and tuffs) interfingers northward with the Beauvoir Formation (slope and platform black mudstones), and covers the Lemaire Formation unconformably. The Yahgan Formation represents an andesitic, volcaniclastic apron, coeval with a Pacific volcanic-arc, filling a marginal basin floored with oceanic crust. The Late Cretaceous compressional orogeny resulted in tectonic inversion, closure of the marginal basin, peak metamorphism and folding, and initial uplifting of the Fuegian Andes. By the latest Cretaceous-earliest Paleogene, the Andes were exposed to subaerial erosion, and the lowest Danian Rı´o Claro Formation bears clear evidence of an Andean clastic provenance. The Rı´o Claro Formation represents the first molasse deposits of the foreland stage of evolution of the Fuegian Andes. Earliest Paleogene north-verging thrust propagation deformed the Rı´o Claro Formation and older units, producing northward depocenter migration. La Despedida Group rests unconformably on the Rı´o Claro Formation and is involved in the thrust and fold belt. Important Eocene compression resulted in thrusting of central Andean basement schists and the Lemaire Formation over Lower Cretaceous and continental Paleogene rocks, respectively. In the

  4. Andes

    Atmospheric Science Data Center

    2013-04-18

    ... Peru, the northern portion of Chile, and the western part of Bolivia, which intersect near the inward "bend" in the coastline. Lake ... whose coastline forms part of the border between Peru and Bolivia, is prominently featured. At an altitude of 12,500 feet, it is said to ...

  5. Andes

    Atmospheric Science Data Center

    2013-04-18

    ... provide a striking demonstration of the power of water erosion. This image pair was acquired by the Multi-angle Imaging ... with the red filter placed over your left eye. Two main erosion formations can be seen. The one above image center is carved by the Rio ...

  6. A millennium of metallurgy recorded by lake sediments from Morococha, Peruvian Andes.

    PubMed

    Cooke, Colin A; Abbott, Mark B; Wolfe, Alexander P; Kittleson, John L

    2007-05-15

    To date, information concerning pre-Colonial metallurgy in South America has largely been limited to the archaeological record of artifacts. Here, we reconstruct a millennium of smelting activity in the Peruvian Andes using the lake-sediment stratigraphy of atmospherically derived metals (Pb, Zn, Cu, Ag, Sb, Bi, and Ti) and lead isotopic ratios (206Pb/ 207Pb) associated with smelting from the Morococha mining region in the central Peruvian Andes. The earliest evidence for metallurgy occurs ca. 1000 A.D., coinciding with the fall of the Wari Empire and decentralization of local populations. Smelting during this interval appears to have been aimed at copper and copper alloys, because of large increases in Zn and Cu relative to Pb. A subsequent switch to silver metallurgy under Inca control (ca. 1450 to conquest, 1533 A.D.) is indicated by increases in Pb, Sb, and Bi, a conclusion supported by further increases of these metals during Colonial mining, which targeted silver extraction. Rapid development of the central Andes during the 20th century raised metal burdens by an order of magnitude above previous levels. Our results represent the first evidence for pre-Colonial smelting in the central Peruvian Andes, and corroborate the sensitivity of lake sediments to pre-Colonial metallurgical activity suggested by earlier findings from Bolivia. PMID:17547165

  7. A millennium of metallurgy recorded by lake sediments from Morococha, Peruvian Andes.

    PubMed

    Cooke, Colin A; Abbott, Mark B; Wolfe, Alexander P; Kittleson, John L

    2007-05-15

    To date, information concerning pre-Colonial metallurgy in South America has largely been limited to the archaeological record of artifacts. Here, we reconstruct a millennium of smelting activity in the Peruvian Andes using the lake-sediment stratigraphy of atmospherically derived metals (Pb, Zn, Cu, Ag, Sb, Bi, and Ti) and lead isotopic ratios (206Pb/ 207Pb) associated with smelting from the Morococha mining region in the central Peruvian Andes. The earliest evidence for metallurgy occurs ca. 1000 A.D., coinciding with the fall of the Wari Empire and decentralization of local populations. Smelting during this interval appears to have been aimed at copper and copper alloys, because of large increases in Zn and Cu relative to Pb. A subsequent switch to silver metallurgy under Inca control (ca. 1450 to conquest, 1533 A.D.) is indicated by increases in Pb, Sb, and Bi, a conclusion supported by further increases of these metals during Colonial mining, which targeted silver extraction. Rapid development of the central Andes during the 20th century raised metal burdens by an order of magnitude above previous levels. Our results represent the first evidence for pre-Colonial smelting in the central Peruvian Andes, and corroborate the sensitivity of lake sediments to pre-Colonial metallurgical activity suggested by earlier findings from Bolivia.

  8. Magnetotelluric Studies of the Laguna del Maule Volcanic Field, Central Chile

    NASA Astrophysics Data System (ADS)

    Cordell, D. R.; Unsworth, M. J.; Diaz, D.; Pavez, M.; Blanco, B.

    2015-12-01

    Geodetic data has shown that the surface of the Laguna del Maule (LdM) volcanic field in central Chile has been moving upwards at rates >20 cm/yr since 2007 over a 200 km2 area. It has been hypothesized that this ground deformation is due to the inflation of a magma body at ~5 km depth beneath the lake (2.8 km b.s.l.). This magma body is a likely source for the large number of rhyolitic eruptions at this location over the last 25 ka. A dense broadband magnetotelluric (MT) array was collected from 2009 to 2015 and included data from a geothermal exploration project. MT phase tensor analysis indicates that the resistivity structure of the region is largely three-dimensional for signals with periods longer than 1 s, which corresponds to depths >5 km. The MT data were inverted using the ModEM inversion algorithm to produce a three-dimensional electrical resistivity model which included topography. Four primary features were identified in the model: 1) A north-south striking, 10 km by 5 km, low-resistivity zone (<5 Ωm) northwest of the inflation centre at a depth of ~5 km (2.8 km b.s.l.) is interpreted as a zone of partial melt which may be supplying material via conduits to account for the observed ground deformation; 2) A shallow low-resistivity feature ~400 m beneath the lake surface (1.8 km a.s.l.) and spatially coincident with the inflation centre is interpreted to be a zone of hydrothermal alteration; 3) A thin, low-resistivity feature to the west of LdM at a depth of ~250 m (2.2 km a.s.l.) is interpreted to be the clay cap of a potential geothermal prospect; 4) A large, low-resistivity zone beneath the San Pedro-Tatara Volcanic Complex to the west of LdM at a depth of ~10 km (8 km b.s.l.) is interpreted to be a zone of partial melt. Further MT data collection is planned for 2016 which will expand the current grid of MT stations to better constrain the lateral extent of the observed features and give greater insight into the dynamics of this restless magma system.

  9. Episodic Cenozoic volcanism and tectonism in the Andes of Peru

    USGS Publications Warehouse

    Noble, D.C.; McKee, E.H.; Farrar, E.; Petersen, U.

    1974-01-01

    Radiometric and geologic information indicate a complex history of Cenozoic volcanism and tectonism in the central Andes. K-Ar ages on silicic pyroclastic rocks demonstrate major volcanic activity in central and southern Peru, northern Chile, and adjacent areas during the Early and Middle Miocene, and provide additional evidence for volcanism during the Late Eocene. A provisional outline of tectonic and volcanic events in the Peruvian Andes during the Cenozoic includes: one or more pulses of igneous activity and intense deformation during the Paleocene and Eocene; a period of quiescence, lasting most of Oligocene time; reinception of tectonism and volcanism at the beginning of the Miocene; and a major pulse of deformation in the Middle Miocene accompanied and followed through the Pliocene by intense volcanism and plutonism. Reinception of igneous activity and tectonism at about the Oligocene-Miocene boundary, a feature recognized in other circum-Pacific regions, may reflect an increase in the rate of rotation of the Pacific plate relative to fixed or quasifixed mantle coordinates. Middle Miocene tectonism and latest Tertiary volcanism correlates with and probably is genetically related to the beginning of very rapid spreading at the East Pacific Rise. ?? 1974.

  10. Active tectonics of the Andes

    NASA Astrophysics Data System (ADS)

    Dewey, J. F.; Lamb, S. H.

    1992-04-01

    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

  11. What do Great Subduction Earthquakes tell us About Continental Deformation of the Upper Plate in the Central Andes Forearc? Insights From Seismotectonics, Continental Deformation and Coulomb Modelisation Along Southern Peru Margin

    NASA Astrophysics Data System (ADS)

    Audin, L.; Perfettini, H.; Tavera, H.

    2007-05-01

    Calientes Fault system (parallel to the trench) and a crustal depth of about 20km. Such a magnitud and crustal depth in the area correlates perfectly with the Quaternary geomorphic evidences of tectonic activity along the Sama-Calientes thrust fault in the forearc in Southern Peru. Some questions are raised by the occurrence of such continental seismicity, just after a major subduction event, as none has been registered in the area since more than 40 years. Continental fault systems constitute a key to the understanding of the forearc deformation in the Arica Elbow, where the Andes obliquity with respect to the Nazca plate convergence direction. Also these results suggest that continental deformation should give us clues to define the pattern of segmentation of the subduction zone by studying seismotectonics and its relation to the segmentation of the upper continental plate.

  12. Glacial recession in the Tropical Andes from the Little Ice Age: the case of Ampato Volcanic Complex (Southern Peru

    NASA Astrophysics Data System (ADS)

    Alcalá, J.; Palacios, D.; Zamorano, J. J.

    2010-03-01

    Data published over the last decade reveal substantial glacial recession in the tropical Andes since the Little Ice Age (LIA), (Ramirez, et al., 2001; Rabatel, et al., 2005; Rabatel, et al., 2008; Vuille, et al., 2008; Hastenrath, 2009; Jomelli, et al., 2009), and a growing rate of recession since the 1980’s caused by global warming (Ramirez, et al., 2001; Vuille, et al., 2008). Today there is great interest in the evolution of these ice masses due to heightened awareness of climate change and of the strategic importance that glaciers have as a hydrologic resource for communities in arid climate zones in the tropical Andes (Mark, 2008; Vuille et al., 2008). Cordillera Blanca forms part of the Andes Mountains of northern Peru, and is a chosen site for many studies on glacier evolution. Vuille et al. 2008 determined that a considerable area of ice mass was lost at Huascarán-Chopicalqui glacier (18% from 1920-1970) and Astesonraju glacier (20% from 1962-2003). Studies at Coropuna volcano, which has the most extensive glacier field in the western range of southern Peru, also report a strong melting trend that began with only minimal recession from 1955-1986 (4%), but increased to 14% from 1986-2007 (Úbeda et al., 2009). Only a few of the Andes glaciers are consistently monitored, and the most comprehensive data are for Chacaltaya and Zongo glaciers (16º S) in Bolivia. Since the maximum LIA, Chacaltaya has lost 89% of its surface area, particularly in recent years. By 1983, the totaled loss was five times the shrinkage for the period 1940-1963 (Ramirez, et al., 2001). Zongo glacier maintained equilibrium from 1956-1975, but later experienced a period dominated by continuous recession (Soruco, et al., 2009). This study expands current knowledge of glacier evolution since the LIA in the Central Volcanic Zone (CVZ; 14º - 27º S) (Stern, 2004) of the Andes. The study site was chosen in an area that had never been used for preliminary research of this type, concretely

  13. Mapping the Interplay of ET and Topography on Precipitation Processes in the Eastern Andes

    NASA Astrophysics Data System (ADS)

    Sun, Xiaoming; Barros, Ana

    2015-04-01

    We present recent work toward elucidating the role of evapotranspiration in the hydrometeorology of the eastern Andes Mountains using realistic and quasi-idealized ET withdrawal experiments with WRF at very high resolution (~1 km grid spacing). The results show that evapotranspiration fluxes modulated by landform govern moist processes in the lower troposphere, including cloud formation and precipitation processes that account for daily precipitation amounts as high as 50-70% depending on synoptic conditions and season. Using parsimonious model experiments and observations for the Amazon basin and the Central Andes, we demonstrate that vegetation acts as a "terrestrial hydrostat" regulating precipitation locally by controlling atmospheric moist instability, and remotely through changes in atmospheric transport patterns. References Sun, X., and A. P. Barros, 2014a: Isolating the role of surface evapotranspiration on moist convection along the eastern flanks of the tropical Andes using a quasi-idealized approach. J. Atmos. Sci., 72, 243-261. Sun, X., and A. P. Barros, 2014b: Impact of Amazonian evapotranspiration on moisture transport and convection along the eastern flanks of the Andes. Q. J. R. Meteorol. Soc., In Review.

  14. Antibacterial Activity, Antioxidant Effect and Chemical Composition of Propolis from the Región del Maule, Central Chile.

    PubMed

    Nina, Nélida; Quispe, Cristina; Jiménez-Aspee, Felipe; Theoduloz, Cristina; Feresín, Gabriela Egly; Lima, Beatriz; Leiva, Elba; Schmeda-Hirschmann, Guillermo

    2015-01-01

    Propolis is commercialized in Chile as an antimicrobial agent. It is obtained mainly from central and southern Chile, but is used for the same purposes regardless of its origin. To compare the antimicrobial effect, the total phenolic (TP), the total flavonoid (TF) content and the phenolic composition, 19 samples were collected in the main production centers in the Región del Maule, Chile. Samples were extracted with MeOH and assessed for antimicrobial activity against Gram (+) and Gram (-) bacteria. TP and TF content, antioxidant activity by the DPPH, FRAP and TEAC methods were also determined. Sample composition was assessed by HPLD-DAD-ESI-MS/MS. Differential compounds in the samples were isolated and characterized. The antimicrobial effect of the samples showed MICs ranging from 31.5 to > 1000 µg/mL. Propolis from the central valley was more effective as antibacterial than those from the coastal area or Andean slopes. The samples considered of interest (MIC ≤ 62.5 µg/mL) showed effect on Escherichia coli, Pseudomonas sp., Yersinia enterocolitica and Salmonella enteritidis. Two new diarylheptanoids, a diterpene, the flavonoids pinocembrin and chrysin were isolated and elucidated by spectroscopic and spectrometric means. Some 29 compounds were dereplicated by HPLC-MS and tentatively identified, including nine flavones/flavonol derivatives, one flavanone, eight dihydroflavonols and nine phenyl-propanoids. Propolis from the Región del Maule showed large variation in antimicrobial effect, antioxidant activity and composition. So far the presence of diarylheptanoids in samples from the coastal area of central Chile can be considered as a marker of a new type of propolis. PMID:26457694

  15. Antibacterial Activity, Antioxidant Effect and Chemical Composition of Propolis from the Región del Maule, Central Chile.

    PubMed

    Nina, Nélida; Quispe, Cristina; Jiménez-Aspee, Felipe; Theoduloz, Cristina; Feresín, Gabriela Egly; Lima, Beatriz; Leiva, Elba; Schmeda-Hirschmann, Guillermo

    2015-10-06

    Propolis is commercialized in Chile as an antimicrobial agent. It is obtained mainly from central and southern Chile, but is used for the same purposes regardless of its origin. To compare the antimicrobial effect, the total phenolic (TP), the total flavonoid (TF) content and the phenolic composition, 19 samples were collected in the main production centers in the Región del Maule, Chile. Samples were extracted with MeOH and assessed for antimicrobial activity against Gram (+) and Gram (-) bacteria. TP and TF content, antioxidant activity by the DPPH, FRAP and TEAC methods were also determined. Sample composition was assessed by HPLD-DAD-ESI-MS/MS. Differential compounds in the samples were isolated and characterized. The antimicrobial effect of the samples showed MICs ranging from 31.5 to > 1000 µg/mL. Propolis from the central valley was more effective as antibacterial than those from the coastal area or Andean slopes. The samples considered of interest (MIC ≤ 62.5 µg/mL) showed effect on Escherichia coli, Pseudomonas sp., Yersinia enterocolitica and Salmonella enteritidis. Two new diarylheptanoids, a diterpene, the flavonoids pinocembrin and chrysin were isolated and elucidated by spectroscopic and spectrometric means. Some 29 compounds were dereplicated by HPLC-MS and tentatively identified, including nine flavones/flavonol derivatives, one flavanone, eight dihydroflavonols and nine phenyl-propanoids. Propolis from the Región del Maule showed large variation in antimicrobial effect, antioxidant activity and composition. So far the presence of diarylheptanoids in samples from the coastal area of central Chile can be considered as a marker of a new type of propolis.

  16. Holocene compression in the Acequión valley (Andes Precordillera, San Juan province, Argentina): Geomorphic, tectonic, and paleoseismic evidence

    NASA Astrophysics Data System (ADS)

    Audemard, M.; Franck, A.; Perucca, L.; Laura, P.; Pantano, Ana; Avila, Carlos R.; Onorato, M. Romina; Vargas, Horacio N.; Alvarado, Patricia; Viete, Hewart

    2016-04-01

    The Matagusanos-Maradona-Acequión Valley sits within the Andes Precordillera fold-thrust belt of western Argentina. It is an elongated topographic depression bounded by the roughly N-S trending Precordillera Central and Oriental in the San Juan Province. Moreover, it is not a piggy-back basin as we could have expected between two ranges belonging to a fold-thrust belt, but a very active tectonic corridor coinciding with a thick-skinned triangular zone, squeezed between two different tectonic domains. The two domains converge, where the Precordillera Oriental has been incorporated to the Sierras Pampeanas province, becoming the western leading edge of the west-verging broken foreland Sierras Pampeanas domain. This latter province has been in turn incorporated into the active deformation framework of the Andes back-arc at these latitudes as a result of enhanced coupling between the converging plates due to the subduction of the Juan Fernández ridge that flattens the Nazca slab under the South American continent. This study focuses on the neotectonics of the southern tip of this N-S elongated depression, known as Acequión (from the homonym river that crosses the area), between the Del Agua and Los Pozos rivers. This depression dies out against the transversely oriented Precordillera Sur, which exhibits a similar tectonic style as Precordillera Occidental and Central (east-verging fold-thrust belt). This contribution brings supporting evidence of the ongoing deformation during the Late Pleistocene and Holocene of the triangular zone bounded between the two leading and converging edges of Precordillera Central and Oriental thrust fronts, recorded in a multi-episodic lake sequence of the Acequión and Nikes rivers. The herein gathered evidence comprise Late Pleistocene-Holocene landforms of active thrusting, fault kinematics (micro-tectonic) data and outcrop-scale (meso-tectonic) faulting and folding of recent lake and alluvial sequences. In addition, seismically

  17. A new species of Eretris Thieme (Lepidoptera: Nymphalidae, Satyrinae) from the Elbow of the Andes region in Bolivia.

    PubMed

    Pyrcz, Tomasz W; Gareca, Yuvinka

    2009-01-01

    A new species of cloud forest butterfly, Eretris julieta n. sp. is described from a region of south-central Bolivia known as the Elbow of the Andes. It is the southernmost known representative of the genus, hitherto known only from a restricted area of interandean valleys in the department of Santa Cruz. Its affinities with other congeners are evaluated.

  18. Early neogene history of the central American arc from Bocas del Toro, western Panama

    USGS Publications Warehouse

    Coates, A.G.; Aubry, M.-P.; Berggren, W.A.; Collins, Luke S.; Kunk, M.

    2003-01-01

    A newly discovered sequence of lower to middle Miocene rocks from the eastern Bocas del Toro archipelago, western Panama, reveals the timing and environment of the earliest stages in the rise of the Isthmus of Panama in this region. Two new formations, the Punta Alegre Formation (lower Miocene, Aquitanian to Burdigalian) and the Valiente Formation (middle Miocene, Langhian to Serravallian), are here named and formally described. The Punta Alegre Formation contains a diagnostic microfauna of benthic and planktic foraminifera and calcareous nannofossils that indicate deposition in a 2000-m-deep pre-isthmian neotropical ocean from as old as 21.5-18.3 Ma. Its lithology varies from silty mudstone to muddy foraminiferal ooze with rare thin microturbidite layers near the top. The Valiente Formation, which ranges in age from 16.4 to ca. 12.0 Ma, lies with slight angular unconformity on the Punta Alegre Formation and consists of five lithofacies: (1) columnar basalt and flow breccia, (2) pyroclastic deposits, (3) coarse-grained volcaniclastic deposits, (4) coral-reef limestone with diverse large coral colonies, and (5) marine debris-flow deposits and microturbidities. These lithofacies are interpreted to indicate that after ca. 16 Ma a volcanic arc developed in the region of Bocas del Toro and that by ca. 12 Ma an extensively emergent archipelago of volcanic islands had formed. 39Ar/40Ar dating of basalt flows associated with the fossiliferous sedimentary rocks in the upper part of the Valiente Formation strongly confirms the ages derived from planktic foraminifera and nannofossils. Paleobathymetric analysis of the two new formations in the Valiente Peninsula and Popa Island, in the Bocas del Toro archipelago, shows a general shallowing from lower- through upper-bathyal to upper-neritic and emergent laharic and fluviatile deposits from ca. 19 to 12 Ma. The overlying nonconformable Bocas del Toro Group contains a lower transgressive sequence ranging from basal nearshore

  19. Pío del Río Ortega: A Pioneer in the Pathology of Central Nervous System Tumors

    PubMed Central

    Ramon y Cajal Agüeras, Santiago

    2016-01-01

    The last 140 years have seen considerable advances in knowledge of central nervous system tumors. However, the main tumor types had already been described during the early years of the twentieth century. The studies of Dr. Pío del Río Hortega have been ones of the most exhaustive histology and cytology-based studies of nervous system tumors. Río Hortega's work was performed using silver staining methods, which require a high level of practical skill and were therefore difficult to standardize. His technical aptitude and interest in nervous system tumors played a key role in the establishment of his classification, which was based on cell lineage and embryonic development. Río Hortega's approach was controversial when he proposed it. Current classifications are not only based on cell type and embryonic lineage, as well as on clinical characteristics, anatomical site, and age. PMID:26973470

  20. Seismicity, fault plane solutions, depth of faulting, and active tectonics of the Andes of Peru, Ecuador, and southern Colombia

    NASA Technical Reports Server (NTRS)

    Suarez, G.; Molnar, P.; Burchfiel, B. C.

    1983-01-01

    The long-period P waveforms observed for 17 earthquakes in the Peruvian Andes during 1963-1976 are compared with synthetic waveforms to obtain fault-plane solutions and focal depths. The morphological units of the Peruvian Andes are characterized: coastal plains, Cordillera Occidental, altiplano and central high plateau, Cordillera Oriental, and sub-Andes. The data base and analysis methodology are discussed, and the results are presented in tables, diagrams, graphs, maps, and photographs illustrating typical formations. Most of the earthquakes are shown to occur in the transition zone from the sub-Andes to the Cordillera Oriental under formations of about 1 km elevation at focal depths of 10-38 km. It is suggested that the sub-Andean earthquakes reflect hinterland deformation of a detached fold and thrust belt, perhaps like that which occurred in parts of the Canadian Rockies. From the total crustal shortening evident in Andean morphology and the shortening rate of the recent earthquakes it is estimated that the topography and crustal root of the Andes have been formed during the last 90-135 Myr.

  1. Hydrological cycles and trends in the NW Argentine Andes since 1940

    NASA Astrophysics Data System (ADS)

    Castino, Fabiana; Bookhagen, Bodo; Strecker, Manfred

    2016-04-01

    Strong spatiotemporal variability characterizes the hydrometeorological pattern in the NW Argentine Andes, draining parts of the most populated and economically important areas of South America. During the summer monsoon season (DJF), the eastern flanks of the central Andes are characterized by deep convection, exposing them to extreme hydrometeorological events. These often result in floods and landslides with disastrous effects on the local populations. Here, we analyze river discharge to explore long-term hydrological variability in NW Argentine Andes and the linked climate controlling processes. We rely on 13 daily river discharge time series relevant to drainage basins spanning several size orders (102-104 km2) starting in 1914 and define different hydro-climate indices both for the mean and the extreme hydrological events. We apply quantile regression to investigate long-term trends and spectral analysis associated with cross-correlation with SST-based climate indices to identify links to large-scale climate variability modes. River discharge presents a pronounced and coherent variability signal in South America, particularly for wide drainage basins, such as the Amazon and Paraná/La Plata rivers, strongly associated to Pacific and Atlantic Oceans Sea Surface Temperature (SST) anomalies (i.e. ENSO, PDO, AMO). Our analysis evidences that in the NW Argentine Andes, mean discharge values are characterized by statistically significant, mostly positive, long-term trends since 1940, whereas the extreme events present a more non-unidirectional trend pattern. Also, coherent multi-annual to multi-decadal cycles characterizing the discharge pattern have been identified, suggesting that processes linked to SST anomaly-modes strongly control the hydrometeorology variability in the NW Argentina Andes.

  2. Preliminary assessment of a Cretaceous-Paleogene Atlantic passive margin, Serrania del Interior and Central Ranges, Venezuela/Trinidad

    SciTech Connect

    Pindell, J.L.; Drake, C.L. ); Pitman, W.C. )

    1991-03-01

    For several decades, Cretaceous arc collision was assumed along northern Venezuela based on isotopic ages of metamorphic minerals. From subsidence histories in Venezuelan/Trinidadian basins, however, it is now clear that the Cretaceous metamorphic rocks were emplaced southeastward as allochthons above an autochthonous suite of rocks in the Cenozoic, and that the pre-Cenozoic autochthonous rocks represent a Mesozoic passive margin. The passive margin rocks have been metamorphosed separately during overthrusting by the allochthons in central Venezuela, but they are uplifted but not significantly metamorphosed in Eastern Venezuela and Trinidad. There, in the Serrania del Interior and Central Ranges of Venezuela/Trinidad, Mesozoic-Paleogene passive margin sequences were uplifted in Neogene time, when the Caribbean Plate arrived from the west and transpressionally inverted the passive margin. Thus, this portion of South America's Atlantic margin subsided thermally without tectonism from Jurassic to Eocene time, and these sections comprise the only Mesozoic-Cenozoic truly passive Atlantic margin in the Western Hemisphere that is now exposed for direct study. Direct assessments of sedimentological, depositional and faunal features indicative of, and changes in, water depth for Cretaceous and Paleogene time may be made here relative to a thermally subsiding passive margin without the complications of tectonism. Work is underway, and preliminary assessments presented here suggest that sea level changes of Cretaceous-Paleogene time are not as pronounced as the frequent large and rapid sea level falls and rises that are promoted by some.

  3. Did growth of high Andes slow down Nazca plate subduction?

    NASA Astrophysics Data System (ADS)

    Quinteros, J.; Sobolev, S. V.

    2010-12-01

    The convergence velocity rate of the Nazca and South-American plate and its variations during the last 100 My are quite well-known from the global plate reconstructions. The key observation is that the rate of Nazca plate subduction has decreased by about 2 times during last 20 Myr and particularly since 10 Ma. During the same time the Central Andes have grown to its present 3-4 km height. Based on the thin-shell model, coupled with mantle convection, it was suggested that slowing down of Nazca plate resulted from the additional load exerted by the Andes. However, the thin-shell model, that integrates stresses and velocities vertically and therefore has no vertical resolution, is not an optimal tool to model a subduction zone. More appropriate would be modeling it with full thermomechanical formulation and self-consistent subduction. We performed a set of experiments to estimate the influence that an orogen like the Andes could have on an ongoing subduction. We used an enhanced 2D version of the SLIM-3D code suitable to simulate the evolution of a subducting slab in a self-consistent manner (gravity driven) at vertical crossections through upper mantle, transition zone and shallower lower mantle. The model utilizes non-linear temperature- and stress-dependant visco-elasto-plastic rheology and phase transitions at 410 and 660 km depth. We started from a reference case with a similar configuration as both Nazca and South-America plates. After some Mys of slow kinematicaly imposed subduction, to develop a coherent thermo-mechanical state, subduction was totally dynamic. On the other cases, the crust was slowly thickened artificially during 10 My to generate the Andean topography. Although our first results show no substantial changes on the velocity pattern of the subduction, we, however, consider this result as preliminary. At the meeting we plan to report completed and verified modeling results and discuss other possible cases of the late Cenozoic slowing down of

  4. Andes Altiplano, Northwest Argentina, South America

    NASA Technical Reports Server (NTRS)

    1993-01-01

    This view of the Andes Altiplano in northwest Argentina (25.5S, 68.0W) is dominated by heavily eroded older and inactive volcano peaks. The altiplano is a high altitude cold desert like the Tibetan Plateau but smaller in area. It is an inland extension of the hyperarid Atacama Desert of the west coast of South America and includes hundreds of volcanic edifices (peaks, cinder cones, lava flows, debris fields, lakes and dry lake beds (salars).

  5. Illicit crops and armed conflict as constraints on biodiversity conservation in the Andes region.

    PubMed

    Fjeldså, Jon; Alvarez, María D; Lazcano, Juan Mario; León, Blanca

    2005-05-01

    Coca, once grown for local consumption in the Andes, is now produced for external markets, often in areas with armed conflict. Internationally financed eradication campaigns force traffickers and growers to constantly relocate, making drug-related activities a principal cause of forest loss. The impact on biodiversity is known only in general terms, and this article presents the first regional analysis to identify areas of special concern, using bird data as proxy. The aim of conserving all species may be significantly constrained in the Santa Marta and Perijá mountains, Darién, some parts of the Central Andes in Colombia, and between the middle Marañón and middle Huallaga valleys in Peru. Solutions to the problem must address the root causes: international drug markets, long-lasting armed conflict, and lack of alternative income for the rural poor.

  6. Illicit crops and armed conflict as constraints on biodiversity conservation in the Andes region.

    PubMed

    Fjeldså, Jon; Alvarez, María D; Lazcano, Juan Mario; León, Blanca

    2005-05-01

    Coca, once grown for local consumption in the Andes, is now produced for external markets, often in areas with armed conflict. Internationally financed eradication campaigns force traffickers and growers to constantly relocate, making drug-related activities a principal cause of forest loss. The impact on biodiversity is known only in general terms, and this article presents the first regional analysis to identify areas of special concern, using bird data as proxy. The aim of conserving all species may be significantly constrained in the Santa Marta and Perijá mountains, Darién, some parts of the Central Andes in Colombia, and between the middle Marañón and middle Huallaga valleys in Peru. Solutions to the problem must address the root causes: international drug markets, long-lasting armed conflict, and lack of alternative income for the rural poor. PMID:16042278

  7. Interseismic Rates From the CTO cGPS Andes and Nepal Networks

    NASA Astrophysics Data System (ADS)

    Genrich, J. F.; Galetzka, J.; Chowdhury, F.; Avouac, J.; Simons, M.; Barrientos, S. E.; Comte, D.; Norabuena, E. O.; Sapkota, S. N.

    2009-12-01

    To study crustal deformation at converging plate margins the Caltech Tectonics Observatory (CTO), together with partner institutions in the host countries, operates continuously observing GPS stations in the central Andes (northern Chile and southern Peru) and in Nepal. The currently 20-site Andes network was established in 2005 with 7 stations. Efforts are underway to provide data streaming links at near real time for the majority of sites. The Nepal network started with 10 sites in 2004 and has been expanded to 23 sites in the last couple of years. Dual frequency code and phase data from all sites are processed with the GAMIT/GLOBK processing package. Reliable interseismic velocities are now available for the majority of sites. Network metadata, rinex data files, processed time series and velocity estimates can be found online thru links at the CTO website: tectonics.caltech.edu.

  8. Jürgen Stock: From One End of the Andes to the Other

    NASA Astrophysics Data System (ADS)

    Vivas, A. K.; Stock, M. J.

    2015-05-01

    Jürgen Stock (1923-2004) will always be remembered for his work on astronomical site testing. He led the efforts to find the best place for CTIO, and his work had a large influence in the setting of other observatories in Chile. He was the first director of CTIO (1963-1966). After his time in Chile, he moved to the other end of the Andes and was in charge of the site selection and the construction of the only professional observatory in Venezuela, the Llano del Hato National Observatory.

  9. Tierra del Fuego, Argentina, South America

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The Mitre Peninsula is the easternmost tip of Tierra del Fuego, Argentina, (54.5S, 65.5W). Early winter snow can be seen on this south tip of the Andes Mountains. These same mountains continue underwater to Antarctica. The Strait of Magellan, separating the South American mainland from Tierra del Fuego is off the scene to the north and west, but the Strait of LeMaire, separating Tierra del Fuego from the Isla de los Estados can be seen.

  10. Thermochronology and tectonics of the Mérida Andes and the Santander Massif, NW South America

    NASA Astrophysics Data System (ADS)

    van der Lelij, Roelant; Spikings, Richard; Mora, Andrés

    2016-04-01

    Pangaea. Triassic extension is documented in the Central Cordillera of Colombia and Ecuador between ~ 240 Ma and ~ 215 Ma, although extension at this time has not been clearly identified in the Mérida Andes or the Santander Massif. Permian to Triassic cooling is not recorded in the structurally isolated Caparo Block in the southern Mérida Andes, suggesting that it may have constituted a distinct fault block in the Triassic. New fission track data from the Santander Massif suggest that it started exhuming at ~ 40 Ma during a period of accelerated convergence between the Nazca/Farallòn Plate and the western margin of South America. Exhumation in the Santander Massif occurred diachronously since ~ 18 Ma in distinct fault blocks at rates of 0.5-1 km/Ma, and may have been driven by east-west compression as a result of the indentation of the Panama-Chocó terrane to western Colombia.

  11. Precipitation variability in the Peruvian Andes under future climatic conditions - Assessment and implications

    NASA Astrophysics Data System (ADS)

    Neukom, Raphael; Rohrer, Mario; Salzmann, Nadine; Calanca, Pierluigi; Huggel, Christian; Acuña, Delia

    2014-05-01

    The Peruvian Andes are characterized by pronounced dry and wet seasons. Agriculture but also other economic sectors such as hydropower production strongly depend on water availability, and are therefore sensitive to changes in precipitation regime at the local and regional scale. Future changes in rainfall amounts and variability may have severe consequences for society and need to be assessed in order to develop adequate strategies for adaptation. The precipitation regime of the high Peruvian Andes is characterized by a complex interplay of local orographic effects with large-scale circulation. A main moisture source for the region is the Amazon Basin and the amount of moisture received in the Central Andes is influenced by the strength of zonal winds in the upper troposphere. As a result, variations in seasonal precipitation amounts can be associated to the South American Monsoon and large-scale teleconnections with the oceans surrounding the South American continent. Notably, however, direct correlations of local precipitation with ENSO, the main driver of tropical Pacific variability, are mostly weak and unstable over the short instrumental period. In this contribution we provide an assessment of future changes in precipitation amounts and variability of the southern Peruvian Andes in relation to changes in the large-scale atmospheric circulation, quantify the associated uncertainties and discuss some of the implications for society. The analysis relies on climate change projections from the CMIP5 initiative. We show that owing to the complex dynamic influence on local climate and the distinct, small-scaled topographic features of the Andes, Global Climate Models (GCMs) have limited ability to adequately simulate precipitation variability at the local scale. Accordingly, uncertainties in simulated precipitation patterns are considerable. More reliable is the simulation of the mid and upper tropospheric flow, as shown by comparing the model output with global re

  12. Changing Student Attitudes using Andes, An Intelligent Homework System

    NASA Astrophysics Data System (ADS)

    van de Sande, Brett; VanLehn, K.; Treacy, D.; Shelby, R.

    2006-12-01

    The size of introductory physics lectures often inhibits personal homework assistance and timely corrective feedback. Andes, an intelligent homework system designed for two semesters of introductory physics, can fill this need by encouraging students to use sound problem solving techniques and providing immediate feedback on each step of a solution. On request, Andes provides principles-based hints based on previous student actions. A multi-year study at the U.S. Naval Academy demonstrate that students using Andes perform better than students working the same problems as graded pencil and paper homeworks. In addition, student attitude surveys show that Andes is preferred over other homework systems. These findings have implications for student attitudes toward, and mastery of, physics. See http://www.andes.pitt.edu for more information.

  13. Changing Student Attitudes using Andes, An Intelligent Homework System

    NASA Astrophysics Data System (ADS)

    van de Sande, Brett; Vanlehn, Kurt; Treacy, Don; Shelby, Bob; Wintersgill, Mary

    2007-03-01

    The size of introductory physics lectures often inhibits personal homework assistance and timely corrective feedback. Andes, an intelligent homework help system designed for two semesters of introductory physics, can fill this need by encouraging students to use sound problem solving techniques and providing immediate feedback on each step of a solution. On request, Andes provides principles-based hints based on previous student actions. A multi-year study at the U.S. Naval Academy demonstrates that students using Andes perform better than students working the same problems as graded pencil and paper homeworks. In addition, student attitude surveys show that Andes is preferred over other homework systems. These findings have implications for student attitudes toward, and mastery of, physics. See http://www.andes.pitt.edu for more information.

  14. The hydrothermal system of the Calabozos caldera, central Chilean Andes

    USGS Publications Warehouse

    Grunder, A.L.; Thompson, J.M.; Hildreth, W.

    1987-01-01

    Active thermal springs associated with the late Pleistocene Calabozos caldera complex occur in two groups: the Colorado group which issues along structures related to caldera collapse and resurgence, and the Puesto Calabozos group, a nearby cluster that is chemically distinct and probably unrelated to the Colorado springs. Most of the Colorado group can be related to a hypothetical parent water containing ???400 ppm Cl at ???250??C by dilution with ???50% of cold meteoric water. The thermal springs in the most deeply eroded part of the caldera were derived from the same parent water by boiling. The hydrothermal system has probably been active for at least as long as 300,000 years, based on geologic evidence and calculations of paleo-heat flow. There is no evidence for economic mineralization at shallow depth. The Calabozos hydrothermal system would be an attractive geothermal prospect were its location not so remote. ?? 1987.

  15. Mount Chacaltaya Regional GAW Station in the Central Andes

    NASA Astrophysics Data System (ADS)

    Zaratti, Francesco; Forno, Ricardo N.; Lolli, Simone

    2010-05-01

    The Mount Chacaltaya Laboratory (MCL), located 30 km from the city of La Paz , at 5300 m asl, is well known as a cosmic ray laboratory that made important contributions to the Elementary Particles Physics in the 40's and 50's of the last century. Since its beginnings, the MCL has also hosted instruments and experiments devoted to atmospheric research and health studies at high altitude locations. In addition, the Chacaltaya glacier has attracted the interest of worldwide climatologists, due to its dramatic retreat. In fact, this glacier does not exist almost anymore. Recently, the Atmospheric Physics Laboratory (LFA-UMSA) has begun to take permanent and field measurements of some relevant atmospheric parameters at MCL, such as carbon dioxide, aerosols and ultraviolet irradiance. In this work we show some characteristics that made Chacaltaya a Regional GAW Station (CHC), recently nominated by WMO. In addition we show some pioneering steps of this project, supported by research institutes from France, Italy, Switzerland and USA. Finally, thanks to the vigorous co-operation of the Raman lidar group at Goddard Space Flight Center, a new YAG Laser is being installed, to be operated together with the "old" Alexandrite Lidar in the study of aerosols at La Paz.

  16. Relationships between mineralization and silicic volcanism in the central Andes

    NASA Technical Reports Server (NTRS)

    Francis, P. W.; Halls, C.; Baker, M. C. W.

    1983-01-01

    Existing models for the genesis of porphyry copper deposits indicate that they formed in granodioritic stocks located in the infrastructure of andesitic stratovolcanoes. It is noted that sites of porphyry-type subvolcanic tin mineralization in the Eastern Cordillera of Bolivia are distinguished by the absence of such andesitic structures. The surface expression of a typical subvolcanic porphyry tin deposit is thought to be an extrusive dome of quartz latite porphyry, sometimes related to a larger caldera structure. Evidence from the El Salvador porphyry copper deposit in the Eocene magmatic belt in Chile indicates that it too may be more closely related to a silicic volcanic structure than to an andesitic stratovolcano. The dome of La Soufriere, Guadeloupe is offered as a modern analog for the surface expression of subvolcanic mineralization processes, with the phreatic eruptions there indicating the formation of hydrothermal breccia bodies in depths. It is pointed out that the occurrence of mineralized porphyries, millions of years after caldera formation, does not necessarily indicate that tin intrusions and mineralization are not genetically related to the subcaldera pluton, but may be a consequence of the long thermal histories (1-10 million years) of the lowermost parts of large plutons.

  17. The Bajada del Diablo astrobleme-strewn field, central Patagonia Argentina: Extending the exploration to surrounding areas

    NASA Astrophysics Data System (ADS)

    Acevedo, R. D.; Rabassa, J.; Ponce, J. F.; Martínez, O.; Orgeira, M. J.; Prezzi, C.; Corbella, H.; González-Guillot, M.; Rocca, M.; Subías, I.; Vásquez, C.

    2012-10-01

    The Bajada del Diablo astrobleme-strewn field is a huge domain of enigmatic circular structures located in central Patagonia. Three more localities are herein described, adding to the first area studied so far. Taking into consideration the four areas, a single, blurred crater dispersion ellipse has been identified. The four sectors now have been investigated, mapped, and georreferenced. Their circular structures, with a total of 185 (some of which are partially obliterated by erosion or sediment accumulation), were identified by remote sensing techniques, but many have been evaluated in situ and interpreted as impact craters. Moreover, two of the structures have been surveyed in detail in the field using a total station instrument. In addition to the previously known occurrence of circular structures on the Eruptive Complex Quiñelaf (Miocene basalts), the Pampa Sastre Fm. (Pliocene conglomerates), and of the Pleistocene pediment gravels and sands, and the geomorphological inferences that have suggested the extra-terrestrial origin of this event, we should now add that the recurrent absence of the cited Pliocene stratigraphic unit at the bottom of the craters is found in the pediment gravel and sands. Its removal has been interpreted as directly related to the impact, according to the magnetometric record of existing magnetic anomalies. Other preliminary observations on the collected samples (glass, breccias, and, most relevant, Fe-Ni-bearing spherules picked up within the impact zones) are herein discussed. Two hypotheses have been put forward about the nature of the possible impacting object that formed these astroblemes which, fragmented into hundreds of pieces, hit the surface of the Earth most likely in middle Pleistocene times. One of these hypotheses is related to the impact of a disintegrated asteroid of the rubble pile type, whereas a second hypothesis refers to the collision of a split comet with the Earth surface. The latter hypothesis is favoured since

  18. Panoramic View of the Andes Mountains, Chile and Argentina

    NASA Technical Reports Server (NTRS)

    1992-01-01

    This panoramic view of the Andes Mountains of Chile and Argentina (24.5S, 69.5W) is dominated by the yellows and browns of the coastal Atacama Desert and the full width of the Andes altiplano, about 300 miles. Winter snow can be seen capping the 22,000 to 23,000 ft. peaks of the Andes. Wisps of cirrus clouds lie over the altiplano and offshore fog obscures the coast. In the distance, the low Chaco Plain appears green with pastures and agriculture.

  19. A case of atmospheric contamination at the slopes of the Los Andes mountain range

    NASA Astrophysics Data System (ADS)

    Romo-Kröger, Carlos M.; Llona, Felipe

    High heavy element contents were found in the aerosol in part of the Chilean central Los Andes mountain range. An important contamination source was found to be the copper mine, El Teniente. Samples were taken with battery-powered Stacked Filter Units (SFU), and sites were reached by using mules. The analysis was done by the PIXE system at the University of Chile. A very definite relation between the distance to El Teniente and the aerosol content of heavy metals (Cu, Zn and As) and sulfur was found. Some discussion about the peculiarity of this sampling and the implications of the results is carried out.

  20. Tectonic geomorphology of the Andes with SIR-A and SIR-B

    NASA Technical Reports Server (NTRS)

    Bloom, Arthur L.; Fielding, Eric J.

    1986-01-01

    Data takes from SIR-A and SIR-B (Shuttle Imaging Radar) crossed all of the principal geomorphic provinces of the central Andes between 17 and 34 S latitude. In conjunction with Thematic Mapping images and photographs from hand-held cameras as well as from the Large Format Camera that was flown with SIR-B, the radar images give an excellent sampling of Andean geomorphology. In particular, the radar images show new details of volcanic rocks and landforms of late Cenozoic age in the Puna, and the exhumed surfaces of tilted blocks of Precambrian crystalline basement in the Sierras Pampeanas.

  1. Use and legacy of mercury in the Andes.

    PubMed

    Cooke, Colin A; Hintelmann, Holger; Ague, Jay J; Burger, Richard; Biester, Harald; Sachs, Julian P; Engstrom, Daniel R

    2013-05-01

    Both cinnabar (HgS) and metallic mercury (Hg(0)) were important resources throughout Andean prehistory. Cinnabar was used for millennia to make vermillion, a red pigment that was highly valued in pre-Hispanic Peru; metallic Hg(0) has been used since the mid-16th century to conduct mercury amalgamation, an efficient process of extracting precious metals from ores. However, little is known about which cinnabar deposits were exploited by pre-Hispanic cultures, and the environmental consequences of Hg mining and amalgamation remain enigmatic. Here we use Hg isotopes to source archeological cinnabar and to fingerprint Hg pollution preserved in lake sediment cores from Peru and the Galápagos Islands. Both pre-Inca (pre-1400 AD) and Colonial (1532-1821 AD) archeological artifacts contain cinnabar that matches isotopically with cinnabar ores from Huancavelica, Peru, the largest cinnabar-bearing district in Central and South America. In contrast, the Inca (1400-1532 AD) artifacts sampled are characterized by a unique Hg isotopic composition. In addition, preindustrial (i.e., pre-1900 AD) Hg pollution preserved in lake sediments matches closely the isotopic composition of cinnabar from the Peruvian Andes. Industrial-era Hg pollution, in contrast, is distinct isotopically from preindustrial emissions, suggesting that pre- and postindustrial Hg emissions may be distinguished isotopically in lake sediment cores. PMID:23597056

  2. Large slope failures in the La Paz basin, Bolivian Andes

    NASA Astrophysics Data System (ADS)

    Roberts, N. J.; Hermanns, R. L.; Rabus, B.; Guzmán, M. A.; Minaya, E.; Clague, J. J.

    2014-12-01

    the La Paz basin provides insights into evolution of the Central Andes and the geologic contribution to the exceptionally high landslide risk in the modern city of La Paz.

  3. Sr and Nd isotopic and trace element compositions of Quaternary volcanic centers of the Southern Andes

    USGS Publications Warehouse

    Futa, K.; Stern, C.R.

    1988-01-01

    Isotopic compositions of samples from six Quaternary volcanoes located in the northern and southern extremities of the Southern Volcanic Zone (SVZ, 33-46??S) of the Andes and from four centers in the Austral Volcanic Zone (AVZ, 49-54??S) range for 87Sr 86Sr from 0.70280 to 0.70591 and for 143Nd 144Nd from 0.51314 to 0.51255. The ranges are significantly greater than previously reported from the southern Andes but are different from the isotopic compositions of volcanoes in the central and northern Andes. Basalts and basaltic andesites from three centers just north of the Chile Rise-Trench triple junction have 87Sr 86Sr, 143Nd 144Nd, La Yb, Ba La, and Hf Lu that lie within the relatively restricted ranges of the basic magmas erupted from the volcanic centers as far north as 35??S in the SVZ of the Andes. The trace element and Sr and Nd isotopic characteristics of these magmas may be explained by source region contamination of subarc asthenosphere, with contaminants derived from subducted pelagic sediments and seawater-altered basalts by dehydration of subducted oceanic lithosphere. In the northern extremity of the SVZ between 33?? and 34??S, basaltic andesites and andesites have higher 87Sr 86Sr, Rb Cs, and Hf Lu, and lower 143Nd 144Nd than basalts and basaltic andesites erupted farther south in the SVZ, which suggests involvement of components derived from the continental crust. In the AVZ, the most primitive sample, high-Mg andesite from the southernmost volcanic center in the Andes (54??S) has Sr and Nd isotopic compositions and K Rb and Ba La similar to MORB. The high La Yb of this sample suggests formation by small degrees of partial melting of subducted MORB with garnet as a residue. Samples from centers farther north in the AVZ show a regionally regular northward increase in SiO2, K2O, Rb, Ba, Ba La, and 87Sr 86Sr and decrease in MgO, Sr, K Rb, Rb Cs, and 143Nd 144Nd, suggesting increasingly greater degrees of fractional crystallization and associated intra

  4. Spatial distribution of rock glaciers in the semi-arid Andes of Argentina

    NASA Astrophysics Data System (ADS)

    Blöthe, Jan Henrik; Halla, Christian; Schrott, Lothar; Götz, Joachim; Trombotto, Dario

    2016-04-01

    Active rock glaciers are indicators for permafrost in periglacial environments of high mountain areas. Within the permafrost body and the seasonally frozen active layer, these rock glaciers potentially store large amounts of water. Especially in semiarid mountain belts, such as the central Andes of Argentina, rock glaciers attain several kilometres in length, covering surface areas of >106 m2. Here, rock glaciers even outrange ice glaciers in cumulative area and absolute number, indicating they might constitute a large water reservoir in this semiarid part of the Andes. Despite their potential hydrological importance, our knowledge about the rock glaciers' spatial distribution, subsurface composition and absolute ice content is still very limited. Our study addresses this shortcoming and aims at assessing the hydrological significance of rock glacier permafrost in the semi-arid Andes of Argentina by combining local geophysical investigations with regional remote sensing analysis. Our research focuses on the central Andes between 30°S and 33°S, where we have compiled an inventory that comprises more than 1200 rock glaciers, as well as 154 clear-ice and debris-covered glaciers. Two field sites that bracket this regional study area towards their northern and southern edge have been selected for local geophysical investigations. At these locations, earlier studies detected the presence of rock glacier permafrost by thermal monitoring and geophysical prospection. Preliminary results of the regional spatial distribution indicate that the spatial density of rock glaciers increases towards the south, concomitant with a twofold increase in mean annual precipitation. Rock glacier density peaks in the area of the Aconcagua massif, while precipitation is further increasing towards the south. Simultaneously, the lower altitudinal limit of intact rock glaciers slightly decreases, with the lowest rock glacier toe positions in the northern study area located at ~3800 m a. s. l

  5. Land Use Change and Hydrologic Processes in High-Elevation Tropical Watersheds of the Northern Andes

    NASA Astrophysics Data System (ADS)

    Avery, W. A.; Riveros-Iregui, D. A.; Covino, T. P.; Peña, C.

    2013-12-01

    The humid tropics cover one-fifth of the Earth's land surface and generate the greatest amount of runoff of any biome globally, but remain poorly understood and understudied. Humid tropical regions of the northern and central Andes have experienced greater anthropogenic land-use/land-cover (LULC) change than nearly any other high mountain system in the world. Vast expanses of this region are currently undergoing rapid transformation to farmland for production of potatoes and pasture for cattle grazing. Although the humid tropics have some of the highest runoff ratios, precipitation, and largest river flows in the world, there is a lack of scientific literature that addresses hydrologic processes in these regions and very few field observations are available to inform management strategies to ensure the sustainability of water resources of present and future generations. We seek to improve understanding of hydrologic processes and feedbacks in the humid tropics using existing and new information from two high-elevation watersheds that span a LULC gradient in the Andes Mountains of Colombia. One site is located in the preserved Chingaza Natural National Park in Central Colombia (undisturbed). The second site is located ~60 km to the northwest and has experienced considerable LULC change over the last 40 years. Combined, these watersheds deliver over 80% of the water resources to Bogotá and neighboring communities. These watersheds have similar climatological characteristics (including annual precipitation), but have strong differences in LULC which result in substantial differences in hydrologic response and streamflow dynamics. We present an overview of many of the pressing issues and effects that land degradation and climate change are posing to the long-term sustainability of water resources in the northern Andes. Our overarching goal is to provide process-based knowledge that will be useful to prevent, mitigate, or respond to future water crises along the Andean

  6. Constraints on deformation of the Southern Andes since the Cretaceous from anisotropy of magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Maffione, Marco; Hernandez-Moreno, Catalina; Ghiglione, Matias C.; Speranza, Fabio; van Hinsbergen, Douwe J. J.; Lodolo, Emanuele

    2015-12-01

    The southernmost segment of the Andean Cordillera underwent a complex deformation history characterized by alternation of contractional, extensional, and strike-slip tectonics. Key elements of southern Andean deformation that remain poorly constrained, include the origin of the orogenic bend known as the Patagonian Orocline (here renamed as Patagonian Arc), and the exhumation mechanism of an upper amphibolite facies metamorphic complex currently exposed in Cordillera Darwin. Here, we present results of anisotropy of magnetic susceptibility (AMS) from 22 sites in Upper Cretaceous to upper Eocene sedimentary rocks within the internal structural domain of the Magallanes fold-and-thrust belt in Tierra del Fuego (Argentina). AMS parameters from most sites reveal a weak tectonic overprint of the original magnetic fabric, which was likely acquired upon layer-parallel shortening soon after sedimentation. Magnetic lineation from 17 sites is interpreted to have formed during compressive tectonic phases associated to a continuous ~ N-S contraction. Our data, combined with the existing AMS database from adjacent areas, show that the Early Cretaceous-late Oligocene tectonic phases in the Southern Andes yielded continuous contraction, variable from ~ E-W in the Patagonian Andes to ~ N-S in the Fuegian Andes, which defined a radial strain field. A direct implication is that the exhumation of the Cordillera Darwin metamorphic complex occurred under compressive, rather than extensional or strike-slip tectonics, as alternatively proposed. If we agree with recent works considering the curved Magallanes fold-and-thrust belt as a primary arc (i.e., no relative vertical-axis rotation of the limbs occurs during its formation), then other mechanisms different from oroclinal bending should be invoked to explain the documented radial strain field. We tentatively propose a kinematic model in which reactivation of variably oriented Jurassic faults at the South American continental margin

  7. A new species of Telmatobius (Amphibia, Anura, Telmatobiidae) from the Pacific slopes of the Andes, Peru.

    PubMed

    Catenazzi, Alessandro; García, Víctor Vargas; Lehr, Edgar

    2015-01-01

    We describe a new species of Telmatobius from the Pacific slopes of the Andes in central Peru. Specimens were collected at 3900 m elevation near Huaytará, Huancavelica, in the upper drainage of the Pisco river. The new species has a snout-vent length of 52.5 ± 1.1 mm (49.3-55.7 mm, n = 6) in adult females, and 48.5 mm in the single adult male. The new species has bright yellow and orange coloration ventrally and is readily distinguished from all other central Peruvian Andean species of Telmatobius but Telmatobiusintermedius by having vomerine teeth but lacking premaxillary and maxillary teeth, and by its slender body shape and long legs. The new species differs from Telmatobiusintermedius by its larger size, flatter head, and the absence of cutaneous keratinized spicules (present even in immature females of Telmatobiusintermedius), and in males by the presence of minute, densely packed nuptial spines on dorsal and medial surfaces of thumbs (large, sparsely packed nuptial spines in Telmatobiusintermedius). The hyper-arid coastal valleys of Peru generally support low species richness, particularly for groups such as aquatic breeding amphibians. The discovery of a new species in this environment, and along a major highway crossing the Andes, shows that much remains to be done to document amphibian diversity in Peru.

  8. A new species of Telmatobius (Amphibia, Anura, Telmatobiidae) from the Pacific slopes of the Andes, Peru

    PubMed Central

    Catenazzi, Alessandro; García, Víctor Vargas; Lehr, Edgar

    2015-01-01

    Abstract We describe a new species of Telmatobius from the Pacific slopes of the Andes in central Peru. Specimens were collected at 3900 m elevation near Huaytará, Huancavelica, in the upper drainage of the Pisco river. The new species has a snout–vent length of 52.5 ± 1.1 mm (49.3–55.7 mm, n = 6) in adult females, and 48.5 mm in the single adult male. The new species has bright yellow and orange coloration ventrally and is readily distinguished from all other central Peruvian Andean species of Telmatobius but Telmatobius intermedius by having vomerine teeth but lacking premaxillary and maxillary teeth, and by its slender body shape and long legs. The new species differs from Telmatobius intermedius by its larger size, flatter head, and the absence of cutaneous keratinized spicules (present even in immature females of Telmatobius intermedius), and in males by the presence of minute, densely packed nuptial spines on dorsal and medial surfaces of thumbs (large, sparsely packed nuptial spines in Telmatobius intermedius). The hyper-arid coastal valleys of Peru generally support low species richness, particularly for groups such as aquatic breeding amphibians. The discovery of a new species in this environment, and along a major highway crossing the Andes, shows that much remains to be done to document amphibian diversity in Peru. PMID:25685025

  9. Seismological Parameters in the Northern Andes, Venezuela

    NASA Astrophysics Data System (ADS)

    Sobiesiak, M.; Palme de Osechas, C.; Choy, J. E.; Morandi S., M. T.; Campo, M.; Granado Ruiz, C.

    2001-12-01

    Venezuelas tectonic setting as part of the plate boundary between the Caribbean and the South American plate causes two major seismologically active fault systems: the roughly west - east trending strike slip fault system along the coast with numerous sub-parallel faults and the Bocono fault system, which dominates the Venezuelan southwest - northeast striking Andes. The main Bocono fault reaches a total length of about 500 km and has a width of approximately 100 km between the southern and northern baseline of the mountain slopes which are marked by inverse faults. This is believed to be due to strain partitioning, a concept which seems to apply as well to the Bocono fault system. The whole fault system is characterized by a high seismicity rate of small scale and intermediate event magnitudes ranging from 1.5 to 6.3 in the last fifty years. In this study we would like to present an investigation on 39 focal mechanism solutions and a b-value mapping of the Andean region with the main goal to throw light on the stess and strain situation. For recompiling the focal memchanisms calculated from first motion polarities, various sources had to been used: seismograms from stations of the local and regional networks of the Seismological Center of ULA, the national seismic network operated by FUNVISIS, the seismic network Lago Maracaibo of PDVSA and the local seismic network of DESURCA. For the b-value mapping we used the two catalogues of ULA and DESURCA of which the last one registered more than 6500 events from 1994 to 1999. The set of focal mechanism solutions studied showed normal, strike slip, and reverse faulting mechanisms concentrated in distinct areas of the Bocono fault system and thus resulting in a zonation also supported by the determinations of the azimuths of the maximum horizontal stress SHmax. This hypothesis of the zonation of the Andes region is strongly supported by the results of the b-value mapping. The zonation as seen in the varying major stress

  10. Landsat Thematic Mapper (TM) Images of the Andes as a Classroom Tool.

    ERIC Educational Resources Information Center

    Bloom, Arthur L.; Fox, Andrew N.

    1990-01-01

    Described is the use of Thematic Mapper images in undergraduate geology instruction. The work of the Andes Project at Cornell University is discussed. Digitally enhanced illustrations of landforms in the Andes mountains of South America are provided. (CW)

  11. 3D Geomodeling of the Venezuelan Andes

    NASA Astrophysics Data System (ADS)

    Monod, B.; Dhont, D.; Hervouet, Y.; Backé, G.; Klarica, S.; Choy, J. E.

    2010-12-01

    The crustal structure of the Venezuelan Andes is investigated thanks to a geomodel. The method integrates surface structural data, remote sensing imagery, crustal scale balanced cross-sections, earthquake locations and focal mechanism solutions to reconstruct fault surfaces at the scale of the mountain belt into a 3D environment. The model proves to be essential for understanding the basic processes of both the orogenic float and the tectonic escape involved in the Plio-Quaternary evolution of the orogen. The reconstruction of the Bocono and Valera faults reveals the 3D shape of the Trujillo block whose geometry can be compared to a boat bow floating over a mid-crustal detachment horizon emerging at the Bocono-Valera triple junction. Motion of the Trujillo block is accompanied by a generalized extension in the upper crust accommodated by normal faults with listric geometries such as for the Motatan, Momboy and Tuñame faults. Extension may be related to the lateral spreading of the upper crust, suggesting that gravity forces play an important role in the escape process.

  12. ANDES Measurements for Advanced Reactor Systems

    NASA Astrophysics Data System (ADS)

    Plompen, A. J. M.; Hambsch, F.-J.; Kopecky, S.; Nyman, M.; Rouki, C.; Salvador Castiñeira, P.; Schillebeeckx, P.; Belloni, F.; Berthoumieux, E.; Gunsing, F.; Lampoudis, C.; Calviani, M.; Guerrero, C.; Cano-Ott, D.; Gonzalez Romero, E.; Aïche, M.; Jurado, B.; Mathieu, L.; Derckx, X.; Farget, F.; Rodrigues Tajes, C.; Bacquias, A.; Dessagne, Ph.; Kerveno, M.; Borcea, C.; Negret, A.; Colonna, N.; Goncalves, I.; Penttilä, H.; Rinta-Antila, S.; Kolhinen, V. S.; Jokinen, A.

    2014-05-01

    A significant number of new measurements was undertaken by the ANDES “Measurements for advanced reactor systems” initiative. These new measurements include neutron inelastic scattering from 23Na, Mo, Zr, and 238U, neutron capture cross sections of 238U, 241Am, neutron induced fission cross sections of 240Pu, 242Pu, 241Am, 243Am and 245Cm, and measurements that explore the limits of the surrogate technique. The latter study the feasibility of inferring neutron capture cross sections for Cm isotopes, the neutron-induced fission cross section of 238Pu and fission yields and fission probabilities through full Z and A identification in inverse kinematics for isotopes of Pu, Am, Cm and Cf. Finally, four isotopes are studied which are important to improve predictions for delayed neutron precursors and decay heat by total absorption gamma-ray spectrometry (88Br, 94Rb, 95Rb, 137I). The measurements which are performed at state-of-the-art European facilities have the ambition to achieve the lowest possible uncertainty, and to come as close as is reasonably achievable to the target uncertainties established by sensitivity studies. An overview is presented of the activities and achievements, leaving detailed expositions to the various parties contributing to the conference.

  13. The first ANDES elements: 9-DOF plate bending triangles

    NASA Technical Reports Server (NTRS)

    Militello, Carmelo; Felippa, Carlos A.

    1991-01-01

    New elements are derived to validate and assess the assumed natural deviatoric strain (ANDES) formulation. This is a brand new variant of the assumed natural strain (ANS) formulation of finite elements, which has recently attracted attention as an effective method for constructing high-performance elements for linear and nonlinear analysis. The ANDES formulation is based on an extended parametrized variational principle developed in recent publications. The key concept is that only the deviatoric part of the strains is assumed over the element whereas the mean strain part is discarded in favor of a constant stress assumption. Unlike conventional ANS elements, ANDES elements satisfy the individual element test (a stringent form of the patch test) a priori while retaining the favorable distortion-insensitivity properties of ANS elements. The first application of this formulation is the development of several Kirchhoff plate bending triangular elements with the standard nine degrees of freedom. Linear curvature variations are sampled along the three sides with the corners as gage reading points. These sample values are interpolated over the triangle using three schemes. Two schemes merge back to conventional ANS elements, one being identical to the Discrete Kirchhoff Triangle (DKT), whereas the third one produces two new ANDES elements. Numerical experiments indicate that one of the ANDES element is relatively insensitive to distortion compared to previously derived high-performance plate-bending elements, while retaining accuracy for nondistorted elements.

  14. Chronologic implications of new Miocene mammals from the Cura-Mallín and Trapa Trapa formations, Laguna del Laja area, south central Chile

    NASA Astrophysics Data System (ADS)

    Flynn, John J.; Charrier, Reynaldo; Croft, Darin A.; Gans, Phillip B.; Herriott, Trystan M.; Wertheim, Jill A.; Wyss, André R.

    2008-12-01

    Recent work in the central Andean Main Range of Chile near Laguna del Laja (˜37.5°S, 71°W) has produced the first mammal fossils for the region. Fossils, locally abundant and well preserved, occur patchily across a wide area southeast of the lake. Mammalian remains are derived from generally strongly folded (kilometer-scale) exposures of the locally ˜1.8 km thick, early to middle Miocene Cura-Mallín Formation; two identifiable specimens have been recovered from the overlying Trapa Trapa Formation as well. Both formations consist primarily of well-stratified (1-5 m thick layers) volcaniclastic and volcanic strata, deposited predominantly in fluviatile systems. The Cura-Mallín Formation is possibly the southern continuation of (or lateral equivalent to) the richly fossiliferous Abanico Formation mapped between ˜32°S and 36°S. Intensive sampling in a series of localities east and south of Laguna del Laja has yielded diverse faunas, in addition to radioisotopically dateable horizons. The new fossil mammal faunas represent as many as six South American Land Mammal "Ages" (SALMAs). Fossils, together with preliminary 40Ar/ 39Ar radioisotopic dates, ranging from ˜9 to 20 Ma across the exposed thickness of the Cura-Mallín Formation and into the overlying Trapa Trapa Formation, provide a robust geochronological framework for middle Cenozoic strata in the Laguna del Laja region. The sequence of directly superposed mammalian assemblages at Laguna del Laja is one of the longest in all of South America, rivaled only by the classic Gran Barranca section of Patagonian Argentina. These data illuminate the geological history of the area and its record of mammalian evolution. The potential to isotopically date these diverse faunas with high precision (error ± 0.5 Ma) presents a rare opportunity to calibrate related portions of the SALMA sequence.

  15. Geologic evolution of the Cordillera Darwin orogenic core complex, Southern Andes

    NASA Astrophysics Data System (ADS)

    Nelson, E. P.

    1981-08-01

    Located in the east-west trending Andes of Tierra del Fuego is a structural culmination exposing deeper crustal levels than in surrounding areas, termed an orogenic core complex because of the localization there of relatively high-grade metamorphism, intense polyphase deformation, and differential uplift. Strongly deformed and regionally metamorphosed pre-Late Jurassic basement rocks mainly of sedimentary origin are unconformably overlain by a cover sequence of Upper Jurassic silicic-intermediate volcanic rocks (Tobifera Formation) and Lower Cretaceous clastic sedimentary rocks (Yahgan Formation). The D1 and D2 phases produced major and minor fold structures, extension and intersection lineations, and axial planar and transposition foliations in complex patterns similar to those in other collision-type orogens. The Darwin and Beagle suites show affinities with S- and I-type granitic suites respectively.

  16. Southern rim of Pacific Ocean basin: southern Andes to southern Alps

    SciTech Connect

    Dalziel, I.W.D.; Garrett, S.W.; Grunow, A.M.; Pankhurst, R.J.; Storey, B.C.; Vennum, W.R.

    1986-07-01

    Between the southern Andes of Tierra del Fuego and the southern Alps of New Zealand lies the least accessible and geologically least explored part of the Pacific Ocean basin. A joint United Kingdom-United States project was initiated in 1983 to elucidate the geologic history and structure of the Pacific margin of Antarctica from the Antarctic Peninsula to Pine Island Bay at approximately lone. 105/sup 0/W. The first season (1983-1984) of this West Antarctic Tectonics Project was spent in the Ellsworth-Whitmore crustal block, and the second (1984-1985) in the Thurston Island crustal block. The project involves structural and general field geology, petrology, geochemistry, paleomagnetism, and airborne geophysics (magnetics and radar ice echo sounding). A final geologic season will be spent in the Pensacola Mountains of the Transantarctic Range in 1987-1988.

  17. Tectonics of the Argentine and Chilean Andes: An introduction

    NASA Astrophysics Data System (ADS)

    Folguera, Andrés; Alvarado, Patricia; Arriagada, César; Ramos, Victor A.

    2015-12-01

    This Special Issue gathers a series of contributions derived from presentations at the 19° Congreso Geológico Argentino held in Córdoba in 2-6 June 2014. Specific subjects cover a wide variety of topics and regions of the Argentine and Chilean Andes, varying from sedimentological analyses and U/Pb dating of detrital zircons in different rocks to determine source areas for different times and regions along the southern Andes; satellite gravity data for monitoring earthquakes at the subduction zone to understand their complex rupture structure; fission track data from the Andes to the foreland region; use of seismic tomographies and conventional seismic reflection data for analyzing crustal structure; to paleomagnetic data and structural and morphological analyses (Fig. 1).

  18. Cenozoic stratigraphy and basin tectonics of the Andes Mountains, 20/sup 0/-28/sup 0/ south latitude

    SciTech Connect

    Jordan, T.E.; Alonso, R.N.

    1987-01-01

    Clastic sedimentary basins have evolved during the past 40 m.y. in the central Andes (lat. 20/sup 0/-28/sub 0/S) in response to shifting patterns of magmatism and deformation. The distribution of these basins and their genetic relations to uplifted areas are analogous to the basins and mountain belts of the North American Rocky Mountains during the Late Cretaceous and early Cenozoic. Petroleum exploration has focused on zones underlying the upper Cenozoic strata along the eastern margin of the Andes mountain belt. Between about 40 and 25 Ma, a nonmarine basin extended across the region that is now the Andes Mountains. Between about 25 and 10 Ma, the western part of the former basin became the site of a volcanic arc; sediment accumulation continued in the east, where marine intercalations demonstrate the low elevation of the basin. After 10 Ma, the volcanic arc remained active and locally widened, and crustal shortening caused regionally important thrust and reverse faulted ranges. During the past 10 m.y., up to 4000 m of coarse clastic debris accumulated in a foreland basin on the eastern flank of the mountains; meanwhile in the interior of the mountains, over 4,0000 m of fine-grained strata and evaporites accumulated in local depocenters. 8 figures.

  19. Cranial vault modification as a cultural artifact: a comparison of the Eurasian steppes and the Andes.

    PubMed

    Torres-Rouff, C; Yablonsky, L T

    2005-01-01

    This paper details the practice of intentional cranial vault modification in the Eurasian steppes as well as in the pre-Columbian Andes focusing on the similarities and differences in how the practice was used to respond to changes in society. The appearance of vault modification in the steppes and the forms seen in the cemeteries of the Syr Darya and Amu Darya River deltas are discussed. Temporal changes in the pattern of modification are also investigated, especially the dramatic homogenization of the custom resulting from the conquests of the Huns. This is contrasted with incidences of cranial modification in the south-central Andes, including the appearance of deliberate head shaping as well as shifts in the practice during the expansion of the Bolivian Altiplano state of Tiwanaku. Similarities in the use of cranial vault modification between these unrelated areas and in the alterations of the practice resulting from foreign contact are considered in light of vault modification's role as a malleable cultural artifact.

  20. New insights into the tectonic evolution of the Boconó Fault, Mérida Andes, Venezuela

    NASA Astrophysics Data System (ADS)

    Backé, G.

    2006-12-01

    The Boconó fault is a major right-lateral strike-slip fault that cuts along strike the Mérida Andes in Venezuela. The uplift of this mountain range started in the Miocene as a consequence of the relative oblique convergence between two lithospheric units named the Maracaibo block to the northwest and the Guyana shield to the southeast. Deformation in the Mérida Andes is partitioned between a strike-slip component along the Boconó fault and shortening perpendicular to the belt. Distinctive features define the Boconó fault: it is shifted southward relative to the chain axis and it does not have a continuous and linear trace but is composed of several fault segments of different orientations striking N35°E to N65°E. Quaternary fault strike-slip motion has been evidenced by various independent studies. However, onset of the strike-slip motion, fault offset and geometry at depth remains a matter of debate. Our work, based on morphostructural analyses of satellite and digital elevation model imagery, provides new data on both the geometry and the tectonic evolution of this major structure. We argue that the Boconó fault affects only the upper crust and connects at depth to a décollement. Consequently, it can not be considered as a plate boundary. The Boconó fault does however form the boundary between two different tectonic areas in the central part of the Mérida Andes as revealed by the earthquake focal mechanisms. South of the Boconó fault, the focal mechanisms are mainly compressional and reverse oblique-slip in agreement with NW SE shortening in the foothills. North of the Boconó fault, extensional and strike-slip deformation dominates. Microtectonic measurements collected in the central part of the Boconó fault are characterized by polyphased tectonics. The dextral shearing along the fault is superimposed to reverse oblique-slip to reverse motion, showing that initiation of transcurrent movement is more likely to have occurred after a certain amount of

  1. The Andes as a peripheral orogen of the breaking-up Pangea

    NASA Astrophysics Data System (ADS)

    Lomize, M. G.

    2008-05-01

    Formation conditions of the peripheral orogen are expressed most fully in the Central Andes, a mountain system almost not yielding in height to the Himalayan-Tibetan system but formed at the margin of ocean without any relations to intercontinental collision. The marine transgression and rejuvenation of subduction in the Early Jurassic during the origination of foldbelt at the margin of Pangea marked the transition to a new supercontinental cycle, and the overall further evolution began and continues now in the frame of the first half of this cycle. The marginal position of this belt above the subduction zone, the rate and orientation of convergence of the lithospheric plates, the age of “absolute” movement of the continental plate, variation in slab velocity, and subduction of heterogeneities of the oceanic crust were the crucial factors that controlled the evolution of the marginal foldbelt. At the stage of initial subsidence (Jurassic-Mid-Cretaceous), during extension of the crust having a moderate thickness (30-35 km), the Andean continental margin comprises the full structural elements of an ensialic island arc that resembled the present-day Sunda system. These conditions changed with the separation and onset of the western drift of the South American continent. Being anchored in the mantle and relatively young, the slab of the Andean subduction zone served as a stop that brought about compression that controlled the subsequent evolution. Due to the contribution of deep magma sources along with marine sediments and products of tectonic erosion removed to a depth, the growth of crust above the subduction zone was favorable for heating of the crust. By the middle Eocene, when compression enhanced owing to the acceleration of subduction, the thermal evolution of the crust had already prepared the transition to the orogenic stage of evolution, i.e., to the progressive viscoplastic shortening and swelling of the mechanically weakened lower crust and the

  2. Magnetic Mineralogy as Indicator of dry Conditions in Lacustrine Sediments From Santa María del Oro, Nayarit, Central Mexico

    NASA Astrophysics Data System (ADS)

    Ortega, B.; Vazquez, G.; Rodriguez, A.

    2007-05-01

    Combined magnetic and geochemical analysis were conducted on laminated sediments from Santa Maria del Oro, a crater lake in Nayarit (Mexico), to build up a model of paleoenvironmental conditions for the late Holocene. The occurrence of a severe drought at the end of the archeological Classic period (100 - 900 AD) has been documented in sites of central Mexico (Zirahuen lake and Lerma basin), the Gulf of Mexico coast (Los Tuxtlas) and the Yucatan peninsula. The effects of this climatic event are considered to have stressed the social and political situation in the Yucatan area and other sites in Mesoamerica, and resulted in the "collapse" of the Maya civilization. Santa Maria del Oro sediments between ca. 600 - 1140 AD are characterized by repeated sequences of ocher silt laminae with high inorganic carbon content, authigenic siderite, and low concentration of SD magnetic minerals, followed upward by an increase of concentrations of fine grained SD and SP ferrimagnetic minerals in brown silt laminae. This sequence is considered to represent dissolution-precipitation cycles of magnetic minerals in low erosion, concentrated waters and anoxic water-sediment interface environments. Dissolution of magnetite occurs in reductive conditions, which are considered as warmer and dryer periods. Above the ocher silt, precipitation of fine grained magnetite occurs when conditions change to oxic environments. Ostracode C and O isotopy document a negative precipitation/evaporation balance during this time period.

  3. Reflections on Andes' Goal-Free User Interface

    ERIC Educational Resources Information Center

    VanLehn, Kurt

    2016-01-01

    Although the Andes project produced many results over its 18 years of activity, this commentary focuses on its contributions to understanding how a goal-free user interface impacts the overall design and performance of a step-based tutoring system. Whereas a goal-aligned user interface displays relevant goals as blank boxes or empty locations that…

  4. Sedimentological evidence for early uplift (Oligocene) of the Venezuelan Andes

    SciTech Connect

    Higgs, R. )

    1993-02-01

    The ongoing Andean orogeny is generally believed to have started in Miocene time. However, sedimentological studies of a Cenozoic clastic section in the northwestern foothills of the Venezuelan Andes (Rio Chama) yield two lines of evidence that uplift was already underway in the Oligocene. (1) Thick Oligocene shales (Leon Formation; 300m) are dark gray and bioturbated. Pyrite is absent and the fauna is restricted to benthonic forms (R. Pittelli), suggesting deposition in a brackish lake rather than the sea. The shales occur throughout the plains northwest of the Andes. Such a large, long-lived lake implies isolation form the sea, suggesting that the Andes were already high in the Oligocene, forming a topographically confined basin similar to the modern Lake Maracaibo. Like modern Lake Maracaibo, there was a tenuous connection with the sea, allowing marine incursions whenever eustatic sea level was high enough, as shown by horizons with marine fossils at other localities. (2) The overlying Oligocene-Miocene succession which caps the Rio Chama section (Caracol Member, Chama Formation; basal Betijoque Formation) includes fluvial channel sands with pebbles which can be matched to Cretaceous cherts of the adjacent Andes (Ftanita de Tachira). The first pebbles appear in the Caracol Member (Oligocene). They are thus regarded as the initial Andean molasse deposits and their deposition has continued to the present day.

  5. Out of the Andes: patterns of diversification in clearwing butterflies.

    PubMed

    Elias, M; Joron, M; Willmott, K; Silva-Brandão, K L; Kaiser, V; Arias, C F; Gomez Piñerez, L M; Uribe, S; Brower, A V Z; Freitas, A V L; Jiggins, C D

    2009-04-01

    Global biodiversity peaks in the tropical forests of the Andes, a striking geological feature that has likely been instrumental in generating biodiversity by providing opportunities for both vicariant and ecological speciation. However, the role of these mountains in the diversification of insects, which dominate biodiversity, has been poorly explored using phylogenetic methods. Here we study the role of the Andes in the evolution of a diverse Neotropical insect group, the clearwing butterflies. We used dated species-level phylogenies to investigate the time course of speciation and to infer ancestral elevation ranges for two diverse genera. We show that both genera likely originated at middle elevations in the Andes in the Middle Miocene, contrasting with most published results in vertebrates that point to a lowland origin. Although we detected a signature of vicariance caused by the uplift of the Andes at the Miocene-Pliocene boundary, most sister species were parapatric without any obvious vicariant barrier. Combined with an overall decelerating speciation rate, these results suggest an important role for ecological speciation and adaptive radiation, rather than simple vicariance.

  6. Andes hantavirus variant in rodents, southern Amazon Basin, Peru.

    PubMed

    Razuri, Hugo; Tokarz, Rafal; Ghersi, Bruno M; Salmon-Mulanovich, Gabriela; Guezala, M Claudia; Albujar, Christian; Mendoza, A Patricia; Tinoco, Yeny O; Cruz, Christopher; Silva, Maria; Vasquez, Alicia; Pacheco, Víctor; Ströher, Ute; Guerrero, Lisa Wiggleton; Cannon, Deborah; Nichol, Stuart T; Hirschberg, David L; Lipkin, W Ian; Bausch, Daniel G; Montgomery, Joel M

    2014-02-01

    We investigated hantaviruses in rodents in the southern Amazon Basin of Peru and identified an Andes virus variant from Neacomys spinosus mice. This finding extends the known range of this virus in South America and the range of recognized hantaviruses in Peru. Further studies of the epizoology of hantaviruses in this region are warranted.

  7. The complete mitochondrial genome of the endemic and threatened killifish Orestias ascotanensis Parenti, 1984 (Cyprinodontiformes, Cyprinodontidae) from the High Andes.

    PubMed

    Quezada-Romegialli, Claudio; Guerrero, Claudia Jimena; Véliz, David; Vila, Irma

    2016-07-01

    The killifish Orestias ascotanensis is endemic to the small isolated springs of Ascotán salt pan in the Central High Andes, Chile. Due to small populations, mining activity, and increasing aridity, this species is catalogued in danger of extinction. The complete mitochondrial genome of O. ascotanesis was assembled with an Ion Torrent sequencer (chip 318) that produced 2.61 million of reads. The 16 617 bp of the entire genome consisted of 22 transfer RNAs, 2 ribosomal RNAs, 13 protein-coding genes, and a control region, showing that the gene composition and arrangement match to that reported for most fishes.

  8. The complete mitochondrial genome of the endemic and threatened killifish Orestias ascotanensis Parenti, 1984 (Cyprinodontiformes, Cyprinodontidae) from the High Andes.

    PubMed

    Quezada-Romegialli, Claudio; Guerrero, Claudia Jimena; Véliz, David; Vila, Irma

    2016-07-01

    The killifish Orestias ascotanensis is endemic to the small isolated springs of Ascotán salt pan in the Central High Andes, Chile. Due to small populations, mining activity, and increasing aridity, this species is catalogued in danger of extinction. The complete mitochondrial genome of O. ascotanesis was assembled with an Ion Torrent sequencer (chip 318) that produced 2.61 million of reads. The 16 617 bp of the entire genome consisted of 22 transfer RNAs, 2 ribosomal RNAs, 13 protein-coding genes, and a control region, showing that the gene composition and arrangement match to that reported for most fishes. PMID:26152352

  9. Convective initiation in the vicinity of the subtropical Andes

    NASA Astrophysics Data System (ADS)

    Rasmussen, K. L.; Houze, R.

    2014-12-01

    Extreme convection tends to form in the vicinity of mountain ranges, and the Andes in subtropical South America help spawn some of the most intense convection in the world. An investigation of the most intense storms for 11 years of TRMM Precipitation Radar (PR) data shows a tendency for squall lines to initiate and develop in this region with the canonical leading convective line/trailing stratiform structure. The synoptic environment and structures of the extreme convection and MCSs in subtropical South America are similar to those found in other regions of the world, especially the United States. In subtropical South America, however, the topographical influence on the convective initiation and maintenance of the MCSs is unique. A capping inversion in the lee of the Andes is important in preventing premature triggering. The Andes and other mountainous terrain of Argentina focus deep convective initiation in a narrow region. Subsequent to initiation, the convection often evolves into propagating mesoscale convective systems similar to those seen over the Great Plains of the U. S. and produces damaging tornadoes, hail, and floods across a wide agricultural region. Numerical simulations conducted with the NCAR Weather Research and Forecasting (WRF) Model extend the observational analysis and provide an objective evaluation of storm initiation, terrain effects, and development mechanisms. The simulated mesoscale systems closely resemble the storm structures seen by the TRMM Precipitation Radar as well as the overall shape and character of the storms shown in GOES satellite data. A sensitivity experiment with different configurations of topography, including both decreasing and increasing the height of the Andes Mountains, provides insight into the significant influence of orography in focusing convective initiation in this region. Lee cyclogenesis and a strong low-level jet are modulated by the height of the Andes Mountains and directly affect the character

  10. Uplift of the Central Andean Plateau and bending of the Bolivian orocline

    NASA Technical Reports Server (NTRS)

    Isaks, Bryan L.

    1988-01-01

    Topographic data are combined with data on structure magmatism, seismicity, and paleomagnetism to support a simple kinematical model for the late Cenozoic evolution of the central Andes. The model interrelates Andean uplift, a changing geometry of the subducted Nazca plate, and a changing outline of the leading edge of the South American plate. It is argued that the late Cenozoic uplift of the Andes is a result of thermal thinning of the lithosphere and crustal thickening produced by crustal shortening.

  11. Diurnal cycle in convergence patterns in the boundary layer east of the Andes and convection

    NASA Astrophysics Data System (ADS)

    Nicolini, Matilde; Skabar, Yanina García

    2011-06-01

    The South American Low-Level Jet Experiment (SALLJEX) provided a unique dataset to investigate the existence of a mesoscale low-level circulation and of a diurnal cycle in its related convergence pattern over the Southeastern South American region east of the Andes, as well as its relationship with deep convection during the warm season. The present paper builds upon high-resolution analyses produced, assimilating the data collected during the SALLJEX field campaign using BRAMS, and explores their capability to reproduce mesoscale circulations not resolved by the low density observational network available in this region. Results of the analyses show a diurnal oscillation signal in the mean boundary layer convergence pattern over the plains with a nocturnal (daytime) convergence (divergence) maximum. These results are coherent with previous findings of a nocturnal phase in the mature stage of organized deep convection and related precipitation in subtropical latitudes east of the Andes during the warm season. The diurnal cycle of convergence/divergence in the boundary layer is described over a 15-day period, during which different synoptic conditions occurred. During weakly forced environments a regime characterized by nocturnal eastward anomaly flow and convergence and daytime westward anomaly flow and divergence related to a mesoscale northwestern mountain-central plain flow regime dominates over the plains between the Andes Mountains, the Parana River Valley, and the southern Brazil mountain range. In contrast, during synoptic conditions dominated by the presence of a deep thermal low over northwestern Argentina and a related low-level jet, convergence at night is mainly accomplished by the predominantly meridional low-level jet, which exhibits an anomalous weak wind speed diurnal cycle with respect to its summer climatological mean. On the other hand daytime divergence is completely produced by the zonal wind component as in the previous synoptic situation

  12. Synchronous interhemispheric Holocene climate trends in the tropical Andes.

    PubMed

    Polissar, Pratigya J; Abbott, Mark B; Wolfe, Alexander P; Vuille, Mathias; Bezada, Maximiliano

    2013-09-01

    Holocene variations of tropical moisture balance have been ascribed to orbitally forced changes in solar insolation. If this model is correct, millennial-scale climate evolution should be antiphased between the northern and southern hemispheres, producing humid intervals in one hemisphere matched to aridity in the other. Here we show that Holocene climate trends were largely synchronous and in the same direction in the northern and southern hemisphere outer-tropical Andes, providing little support for the dominant role of insolation forcing in these regions. Today, sea-surface temperatures in the equatorial Pacific Ocean modulate rainfall variability in the outer tropical Andes of both hemispheres, and we suggest that this mechanism was pervasive throughout the Holocene. Our findings imply that oceanic forcing plays a larger role in regional South American climate than previously suspected, and that Pacific sea-surface temperatures have the capacity to induce abrupt and sustained shifts in Andean climate. PMID:23959896

  13. First human isolate of Hantavirus (Andes virus) in the Americas.

    PubMed

    Galeno, Hector; Mora, Judith; Villagra, Eliecer; Fernandez, Jorge; Hernandez, Jury; Mertz, Gregory J; Ramirez, Eugenio

    2002-07-01

    We isolated Andes virus (formal name: Andes virus [ANDV], a species in the genus Hantavirus), from serum of an asymptomatic 10-year-old Chilean boy who died 6 days later of hantavirus pulmonary syndrome (HPS). The serum was obtained 12 days after his grandmother died from HPS and 2 days before he became febrile. No hantavirus immunoglobulin (Ig) G or IgM antibodies were detected in the serum sample. After three blind passages, ANDV antigens were detected in Vero E6 cells by immunofluorescence assay and enzyme-linked immunosorbent assay, and ANDV RNA was detected by reverse transcription-polymerase chain reaction. A fragment of the virus genome showed 96.2% nucleotide identity with that of prototype ANDV. To our knowledge, this is the first isolation of any agent of hemorrhagic fever with HPS from a human and the first such isolation of hantavirus before symptoms of that syndrome or HPS began.

  14. First GPS baseline results from the North Andes

    NASA Technical Reports Server (NTRS)

    Kellogg, James N.; Freymueller, Jeffrey T.; Dixon, Timothy H.; Neilan, Ruth E.; Ropain, Clemente

    1990-01-01

    The CASA Uno GPS experiment (January-February 1988) has provided the first epoch baseline measurements for the study of plate motions and crustal deformation in and around the North Andes. Two dimensional horizontal baseline repeatabilities are as good as 5 parts in 10 to the 8th for short baselines (100-1000 km), and better than 3 parts in 10 to the 8th for long baselines (greater than 1000 km). Vertical repeatabilities are typically 4-6 cm, with a weak dependence on baseline length. The expected rate of plate convergence across the Colombia Trench is 6-8cm/yr, which should be detectable by the repeat experiment planned for 1991. Expected deformation rates within the North Andes are of the order of 1 cm/yr, which may be detectable with the 1991 experiment.

  15. Glacier shrinkage and water resources in the Andes

    NASA Astrophysics Data System (ADS)

    Francou, Bernard; Coudrain, Anne

    For more than a century glaciers around the world have been melting as air temperatures rise due to a combination of natural processes and human activity. The disappearance of these glaciers can have wide-ranging effects, such as the creation of new natural hazards or changes in stream flow that could threaten water suppliesSome of the most dramatic melting has occurred in the Andes mountain range in South America. To highlight the climatic and glacial change in the Andes and to encourage the scientific community to strengthen the glacier observation network that stretches from Colombia to the Patagonian ice fields, the Instituto Nacional de Recursos Naturales (INRENA), Perú, and the Institute of Research and Development (IRD), France, recently organized the second Symposium on Mass Balance of Andean Glaciers in Huaráz,Perú.

  16. Synchronous interhemispheric Holocene climate trends in the tropical Andes

    PubMed Central

    Polissar, Pratigya J.; Abbott, Mark B.; Wolfe, Alexander P.; Vuille, Mathias; Bezada, Maximiliano

    2013-01-01

    Holocene variations of tropical moisture balance have been ascribed to orbitally forced changes in solar insolation. If this model is correct, millennial-scale climate evolution should be antiphased between the northern and southern hemispheres, producing humid intervals in one hemisphere matched to aridity in the other. Here we show that Holocene climate trends were largely synchronous and in the same direction in the northern and southern hemisphere outer-tropical Andes, providing little support for the dominant role of insolation forcing in these regions. Today, sea-surface temperatures in the equatorial Pacific Ocean modulate rainfall variability in the outer tropical Andes of both hemispheres, and we suggest that this mechanism was pervasive throughout the Holocene. Our findings imply that oceanic forcing plays a larger role in regional South American climate than previously suspected, and that Pacific sea-surface temperatures have the capacity to induce abrupt and sustained shifts in Andean climate. PMID:23959896

  17. High Altiplano of the Andes, Chile and Argentina

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The dry desert climate of the high Altiplano of the South american Andes (27.0S, 68.5W) presents a stark landscape of lava flows from many extinct volcanoes and salars (dry lakebeds). Wind streaks across the surface are the result of strong prevailing WNW winds picking up fine particles of salt and volcanic ash, transporting it eastward. The small lakes in some of the basins have different colors because of varying salinity and algae activity.

  18. Glaciers in Southern Andes seen from STS-63 Discovery

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Glaciers in the Andes Mountains jut into two lakes in the Patagoinian lowlands. Lago Viedman appears at center in the top portion of the 70mm frame. Lago Argentina barely appears in the frame at far right. The glaciers descend from the very high and wet mountains of southern Chile (peaks reach 3,600 meters) in a range locally known as Cordillera Darwin. The lakes in the picture were carved out by the glaciers during advances of the ice.

  19. Reconstruction of Late Cretaceous Magmatic Arcs in the Northern Andes: Single Versus Multiple Arc Systems

    NASA Astrophysics Data System (ADS)

    Cardona, A.; Jaramillo, J. S.; Leon, S.; Hincapie, S.; Mejia, D.; Patino, A. M.; Vanegas, J.; Zapata, S.; Valencia, V.; Jimenez, G.; Monsalve, G.

    2014-12-01

    Although magmatic rocks are major tracers of the geological evolution of convergent margins, pre-collisional events such as subduction erosion, collisional thrusting or late collisional strike slip segmentation may difficult the recognizing of multiple arc systems and therefore the existence of paleogeographic scenarios with multiple subduction systems. New field, U-Pb geochronology and whole rock geochemistry constraints from the northwestern segment of the Central Cordillera in the states of Antioquia and Caldas (Colombia) are used to understand the nature of the Late Cretaceous arc magmatism and evaluate the existence of single or multiple Pacific and Caribbean arc systems in the growth of the Northwestern Andes. The new results integrated with additional field and published information is used to suggest the existence of at least three different magmatic arcs. (1) An Eastern Continental arc built within a well defined Permian to Triassic continental crust that record a protracted 90-70 Ma magmatic evolution, (2) a 90-80 arc formed within attenuated continental crust and associated oceanic crust, (3) 90-88 Ma arc formed over a Late Cretaceous plateau crust. The eastern arcs were formed as part of double eastern vergent subduction system, where the most outboard arc represent a fringing arc formed over detached fragments of continental crust, whereas the easternmost continental arc growth by the closure an subduction of and older and broad Triassic to Early Jurassic back-arc ocean. Its closure also end up in ophiolite emplacement. The third allochtonous oceanic arc was formed over the Caribbean plateau crust and was accreted to the continental margin in the Late Cretaceous. Ongoing paleomagnetic, deformational, gravimetric and basin analysis will be integrate to test this model and understand the complex Late Cretaceous tectonic evolution of the Northern Andes.

  20. Geochemical composition of river loads in the Tropical Andes: first insights from the Ecuadorian Andes

    NASA Astrophysics Data System (ADS)

    Tenorio Poma, Gustavo; Govers, Gerard; Vanacker, Veerle; Bouillon, Steven; Álvarez, Lenín; Zhiminaicela, Santiago

    2015-04-01

    Processes governing the transport of total suspended material (TSM), total dissolved solids (TDS) and particulate organic carbon (POC) are currently not well known for Tropical Andean river systems. We analyzed the geochemical behavior and the budgets of the particulate and dissolved loads for several sub-catchments in the Paute River basin in the southern Ecuadorian Andes, and examined how anthropogenic activities influenced the dynamics of riverine suspended and dissolved loads. We gathered a large dataset by regularly sampling 8 rivers for their TSM, POC, and TDS. Furthermore, we determined the major elements in the dissolved load and stable isotope composition (δ13C) of both the POC, and the dissolved inorganic carbon (DIC). The rivers that were sampled flow through a wide range of land uses including: 3 nature conservation areas (100 - 300 Km²), an intensive grassland and arable zone (142 Km²); downstream of two cities (1611 and 443 Km²), and 2 degraded basins (286 and 2492 Km²). We described the geochemical characteristics of the river loads both qualitatively and quantitatively. Important differences in TSM, POC and TDS yields were found between rivers: the concentration of these loads increases according with human activities within the basins. For all rivers, TSM, TDS and POC concentrations were dependent on discharge. Overall, a clear relation between TSM and POC (r²=0.62) was observed in all tributaries. The C:N ratios and δ13CPOC suggest that the POC in most rivers is mainly derived from soil organic matter eroded from soils dominated by C3 vegetation (δ13CPOC < -22‰). Low Ca:Si ratios (<1)and high δ13CDIC (-9 to -4) in the Yanuncay, Tomebamba1 and Machángara, rivers suggest that weathering of silica rocks is dominant in these catchments, and that the DIC is mainly derived from the soil or atmospheric CO2. In contrast, the Ca:Si ratio was high for the Burgay and Jadán rivers (1-13), and the low δ13CDIC values (-9 to -15) suggest that

  1. Is tourism damaging ecosystems in the Andes? Current knowledge and an agenda for future research.

    PubMed

    Barros, Agustina; Monz, Christopher; Pickering, Catherine

    2015-03-01

    Despite the popularity of tourism and recreation in the Andes in South America and the regions conservation value, there is limited research on the ecological impacts of these types of anthropogenic use. Using a systematic quantitative literature review method, we found 47 recreation ecology studies from the Andes, 25 of which used an experimental design. Most of these were from the Southern Andes in Argentina (13 studies) or Chile (eight studies) with only four studies from the Northern Andes. These studies documented a range of impacts on vegetation, birds and mammals; including changes in plant species richness, composition and vegetation cover and the tolerance of wildlife of visitor use. There was little research on the impacts of visitors on soils and aquatic systems and for some ecoregions in the Andes. We identify research priorities across the region that will enhance management strategies to minimise visitor impacts in Andean ecosystems.

  2. A phytosociological analysis and synopsis of the dry woodlands and succulent vegetation of the Peruvian Andes.

    PubMed

    Galán-DE-Mera, Antonio; Sánchez-Vega, Isidoro; Linares-Perea, Eliana; Campos, José; Montoya, Juan; Vicente-Orellana, José A

    2016-01-01

    A phytosociological approach to dry forest and cactus communities on the occidental slopes of the Peruvian Andes is presented in base of 164 plots carried out following the Braun-Blanquet method. From them, 52 have been made recently, and the other 112 were taken from the literature. After a multivariate analysis, using a hierarchical clustering and a detendred correspondence analysis, the Acacio-Prosopidetea class (dry forest and cactus communities, developed on soils with some edaphic humidity or precipitations derived from El Niño Current), the Opuntietea sphaericae class (cactus communities of central and southern Peru, on few stabilized rocky or sandy soils) and the Carico-Caesalpinietea class (dry forests of the Peruvian coastal desert, influenced by the maritime humidity of the cold Humboldt Current), are differentiated. Within the Acacio-Prosopidetea class, two alliances are commented: the Bursero-Prosopidion pallidae (with two new associations Loxopterygio huasanginis-Neoraimondietum arequipensis and Crotono ruiziani-Acacietum macracanthae), and the new alliance Baccharido-Jacarandion acutifoliae (with the new associations Armatocereo balsasensis-Cercidietum praecocis and Diplopterydo leiocarpae-Acacietum macracanthae). For the Opuntietea sphaericae class, the association Haageocereo versicoloris-Armatocereetum proceri (Espostoo-Neoraimondion) is described on the basis of plots from hyperarid localities of central Peru. Finally, a typological classification of the studied plant communities is given. PMID:27142545

  3. Distribution models and species discovery: the story of a new Solanum species from the Peruvian Andes.

    PubMed

    Särkinen, Tiina; Gonzáles, Paúl; Knapp, Sandra

    2013-01-01

    A new species of Solanum sect. Solanum from Peru is described here. Solanum pseudoamericanum Särkinen, Gonzáles & S.Knapp sp. nov. is a member of the Morelloid clade of Solanum, and is characterized by the combination of mostly forked inflorescences, flowers with small stamens 2.5 mm long including the filament, and strongly exerted styles with capitate stigmas. The species was first thought to be restricted to the seasonally dry tropical forests of southern Peru along the dry valleys of Río Pampas and Río Apurímac. Results from species distribution modelling (SDM) analysis with climatic predictors identified further potential suitable habitat areas in northern and central Peru. These areas were visited during field work in 2013. A total of 17 new populations across the predicted distribution were discovered using the model-based sampling method, and five further collections were identified amongst herbarium loans. Although still endemic to Peru, Solanum pseudoamericanum is now known from across northern, central and southern Peru. Our study demonstrates the usefulness of SDM for predicting new occurrences of rare plants, especially in the Andes where collection densities are still low in many areas and where many new species remain to be discovered. PMID:24399901

  4. Distribution models and species discovery: the story of a new Solanum species from the Peruvian Andes

    PubMed Central

    Särkinen, Tiina; Gonzáles, Paúl; Knapp, Sandra

    2013-01-01

    Abstract A new species of Solanum sect. Solanum from Peru is described here. Solanum pseudoamericanum Särkinen, Gonzáles & S.Knapp sp. nov. is a member of the Morelloid clade of Solanum, and is characterized by the combination of mostly forked inflorescences, flowers with small stamens 2.5 mm long including the filament, and strongly exerted styles with capitate stigmas. The species was first thought to be restricted to the seasonally dry tropical forests of southern Peru along the dry valleys of Río Pampas and Río Apurímac. Results from species distribution modelling (SDM) analysis with climatic predictors identified further potential suitable habitat areas in northern and central Peru. These areas were visited during field work in 2013. A total of 17 new populations across the predicted distribution were discovered using the model-based sampling method, and five further collections were identified amongst herbarium loans. Although still endemic to Peru, Solanum pseudoamericanum is now known from across northern, central and southern Peru. Our study demonstrates the usefulness of SDM for predicting new occurrences of rare plants, especially in the Andes where collection densities are still low in many areas and where many new species remain to be discovered. PMID:24399901

  5. A phytosociological analysis and synopsis of the dry woodlands and succulent vegetation of the Peruvian Andes.

    PubMed

    Galán-DE-Mera, Antonio; Sánchez-Vega, Isidoro; Linares-Perea, Eliana; Campos, José; Montoya, Juan; Vicente-Orellana, José A

    2016-01-01

    A phytosociological approach to dry forest and cactus communities on the occidental slopes of the Peruvian Andes is presented in base of 164 plots carried out following the Braun-Blanquet method. From them, 52 have been made recently, and the other 112 were taken from the literature. After a multivariate analysis, using a hierarchical clustering and a detendred correspondence analysis, the Acacio-Prosopidetea class (dry forest and cactus communities, developed on soils with some edaphic humidity or precipitations derived from El Niño Current), the Opuntietea sphaericae class (cactus communities of central and southern Peru, on few stabilized rocky or sandy soils) and the Carico-Caesalpinietea class (dry forests of the Peruvian coastal desert, influenced by the maritime humidity of the cold Humboldt Current), are differentiated. Within the Acacio-Prosopidetea class, two alliances are commented: the Bursero-Prosopidion pallidae (with two new associations Loxopterygio huasanginis-Neoraimondietum arequipensis and Crotono ruiziani-Acacietum macracanthae), and the new alliance Baccharido-Jacarandion acutifoliae (with the new associations Armatocereo balsasensis-Cercidietum praecocis and Diplopterydo leiocarpae-Acacietum macracanthae). For the Opuntietea sphaericae class, the association Haageocereo versicoloris-Armatocereetum proceri (Espostoo-Neoraimondion) is described on the basis of plots from hyperarid localities of central Peru. Finally, a typological classification of the studied plant communities is given.

  6. Detrital Record of the Middle to Late Paleozoic Transition from Subduction to Collision in the Northern Andes: Implications in the Paleogeographic Reconstructions of Pangea

    NASA Astrophysics Data System (ADS)

    Valencia, V.; Cardona, A.

    2014-12-01

    Discriminating between these type of orogens and understanding the transition between subduction and collision in the Northern Andes remains elusive and controversial due to the apparent yuxtaposition of Central and South American terranes within Pangea reconstruction. New U-Pb detrital zircon geochronology from Late Paleozoic sedimentary and meta-sedimentary rocks from the Eastern Cordillera of the Colombian Andes (Santander and Flortesta Massif) were obtained and used to discriminate changes in the relative intensity of magmatic activity and refine the timing of sedimentary accumulation and metamorphism and their relation with tectonic models. The U-Pb LA-ICP-MS results suggest that Early Devonian magmatism is significantly more limited than the former Ordovician to Silurian record and that sedimentation and metamorphism in the Eastern Cordillera of the Colombian Andes is of Late Paleozoic age. We related the major changes in the magmatic input to the Late Paleozoic sedimentary basin as a tracer of the major changes in convergence between Laurentia and Gondwana, that formed an extremely oblique convergent margin between the Devonian and the Carboniferous until the Late Carboniferous metamorphism that end with Pangea agglutination.

  7. New isotopic ages and the timing of orogenic events in the Cordillera Darwin, southernmost Chilean Andes

    NASA Astrophysics Data System (ADS)

    Hervé, F.; Nelson, E.; Kawashita, K.; Suárez, M.

    1981-10-01

    The Cordillera Darwin, a structural culmination in the Andes of Tierra del Fuego, exposes an orogenic core zone that has undergone polyphase deformation and metamorphism. Some of the classic problems of orogenic zones have remained unanswered in the Cordillera Darwin: the age of deformed plutonic rocks, the distinction of structurally reactivated basement and metamorphosed cover rocks, and the timing of orogenic events. This study addresses and partially answers these questions. A well-constrained Rb-Sr isochron age of157±8m.y. and an initial 87Sr/ 86Sr ratio of 0.7087 obtained from a pre-tectonic granitic suite suggest a genetic relation between this suite and Upper Jurassic silicic volcanic rocks in the cover sequence (Tobifera Formation), and also suggest involvement of continental crust in formation of these magmas. A poorly constrained Rb-Sr isochron age of240±40m.y. obtained from supposed basement schists is consistent with field relations in the area which suggest a late Paleozoic/early Mesozoic metamorphism for these pre-Late Jurassic rocks. However, because of scatter in the data and the uncertainties involved in dating metasedimentary rocks, the significance of the isotopic age is dubious. Compilation of previously published ages in the area [9] with new mineral ages reported here indicate that "early Andean" orogenic events occurred between 100 and 84 m.y. ago, and that subduction-related magmatism has contributed, probably discontinuously, to the crustal evolution of the region throughout the Mesozoic.

  8. Stratigraphic and Petrological Constraints of Cretaceous Subduction Initiation and Arc-Continent Collision in the Northern Andes

    NASA Astrophysics Data System (ADS)

    Leon, S.; Cardona, A.; Mejia, D.; Parra, M.

    2014-12-01

    Middle to Late-Cretaceous orogenic events in the northern Andes have been commonly reconstructed from the analysis of inland basins or the integration of regional scale thermochronological, geochronological and geochemical datasets from the accreted blocks. In contrast, limited studies have been developed on the stratigraphic and deformational record of magmatic and sedimentary sequences exposed near the suture zones. New field and petrologic data are used to characterize an ophiolite type sequence that outcrops in the western flank from the northwestern segment of the Central Cordillera of Colombia. Stratigraphic analysis indicate the existence of Albian-Aptian deep marine pelitic sequence interbedded with minor chert and thin quartz sandstone beds that apparently change to a volcanic dominate stratigraphy. Deformed ophiolite-like mafic and ultramafic plutonic rocks and isolated pillow lavas are also exposed to the east in fault contact with the pelitic sequence. The pelitic and interlayered volcanic rocks represent the growth of an extensional Early-Cretaceous basin that followed a Late-Jurassic magmatic quiescence in the Northern Andes. The volcano-sedimentary record is probably related to the growth of a fore-arc basin in a new subduction zone that extends until the Late Cretaceous. The deformation and obduction of the ophiolitic association and the fore-arc basin were probably triggered by the Late Cretaceous collision with an allocthonous plateau-arc associated to the migration of the Caribbean plate.

  9. Transmission Study of Andes Hantavirus Infection in Wild Sigmodontine Rodents†

    PubMed Central

    Padula, P.; Figueroa, R.; Navarrete, M.; Pizarro, E.; Cadiz, R.; Bellomo, C.; Jofre, C.; Zaror, L.; Rodriguez, E.; Murúa, R.

    2004-01-01

    Our study was designed to contribute to an understanding of the timing and conditions under which transmission of Andes hantavirus in Oligoryzomys longicaudatus reservoir populations takes place. Mice were caged in test habitats consisting of steel drums containing holding cages, where seronegative rodents were exposed to wild seropositive individuals by freely sharing the same cage or being separated by a wire mesh. Tests were also performed for potential viral transmission to mice from excrement-tainted bedding in the cages. Andes virus transmitted efficiently; from 130 attempts with direct contact, 12.3% resulted in virus transmission. However, if we consider only those rodents that proved to be infectious, from 93 attempts we obtained 16 infected animals (17.2%). Twelve of them resulted from intraspecies O. longicaudatus encounters where male mice were differentially affected and 4 resulted from O. longicaudatus to Abrothrix olivaceus. Experiments using Abrothrix longipilis as receptors were not successful. Transmission was not observed between wire mesh-separated animals, and mice were not infected from excrement-tainted bedding. Bites seemed not to be a requisite for oral transmission. Genomic viral RNA was amplified in two out of three saliva samples from seropositive rodents, but it was not detected in urine samples obtained by vesicle puncture from two other infected rodents. Immunohistochemistry, using antibodies against Andes (AND) hantavirus proteins, revealed strong reactions in the lung and salivary glands, supporting the possibility of oral transmission. Our study suggests that AND hantavirus may be principally transmitted via saliva or saliva aerosols rather than via feces and urine. PMID:15479837

  10. Early local last glacial maximum in the tropical Andes.

    PubMed

    Smith, Jacqueline A; Seltzer, Geoffrey O; Farber, Daniel L; Rodbell, Donald T; Finkel, Robert C

    2005-04-29

    The local last glacial maximum in the tropical Andes was earlier and less extensive than previously thought, based on 106 cosmogenic ages (from beryllium-10 dating) from moraines in Peru and Bolivia. Glaciers reached their greatest extent in the last glacial cycle approximately 34,000 years before the present and were retreating by approximately 21,000 years before the present, implying that tropical controls on ice volumes were asynchronous with those in the Northern Hemisphere. Our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures, which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle.

  11. Direction and timing of uplift propagation in the Peruvian Andes deduced from molecular phylogenetics of highland biotaxa

    NASA Astrophysics Data System (ADS)

    Picard, Damien; Sempere, Thierry; Plantard, Olivier

    2008-07-01

    Physical paleoaltimetric methods are increasingly used to estimate the amount and timing of surface uplift in orogens. Because the rise of mountains creates new ecosystems and triggers evolutionary changes, biological data may also be used to assess the development and timing of regional surface uplift. Here we apply this idea to the Peruvian Andes through a molecular phylogeographic and phylochronologic analysis of Globodera pallida, a potato parasite nematode that requires cool temperatures and thus thrives above 2.0-2.5 km in these tropical highlands. The Peruvian populations of this species exhibit a clear evolutionary pattern with deeper, more ancient lineages occurring in Andean southern Peru and shallower, younger lineages occurring progressively northwards. Genetically diverging G. pallida populations thus progressively colonized highland areas as these were expanding northwards, demonstrating that altitude in the Peruvian Andes was acquired longitudinally from south to north, i.e. in the direction of decreasing orogenic volume. This phylogeographic structure is recognized in other, independent highland biotaxa, and point to the Central Andean Orocline (CAO) as the region where high altitudes first emerged. Moreover, molecular clocks relative to Andean taxa, including the potato-tomato group, consistently estimate that altitudes high enough to induce biotic radiation were first acquired in the Early Miocene. After calibration by geological and biological tie-points and intervals, the phylogeny of G. pallida is used as a molecular clock, which estimates that the 2.0-2.5 km threshold elevation range was reached in the Early Miocene in southernmost Peru, in the Middle and Late Miocene in the Abancay segment (NW southern Peru), and from the latest Miocene in central and northern Peru. Although uncertainties attached to phylochronologic ages are significantly larger than those derived from geochronological methods, these results are fairly consistent with coeval

  12. Transferring Knowledge Gained From a Field Experience in Tierra del Fuego, the Uttermost Part of the Earth, to Central Texas Science Classrooms

    NASA Astrophysics Data System (ADS)

    Ormiston, C.; Dovzak, N.; Anderson, S.; Perry, E.; Ellins, K.; Tingle, D.; Knettel, P.; Redding, S.; Odle, K.

    2005-12-01

    As part of the UTIG's Teachers in the Field program, we, three teachers from Boerne High School in south-central Texas, and four of our students, collaborated with an international team of geoscientists studying the tectonic and climatic evolution of the Lago Fagnano region in Tierra del Fuego, Argentina, in March 2005. This unique field experience allowed us to participate in all aspects of the scientific process: the consideration of research questions, development of a research plan, collection of field data and observations, and synthesis and presentation of results. In addition to field work and reconnaissance tied directly to the project objectives, we characterized the modern chemical/physical soil and water parameters (temperature, pH, dissolved oxygen, NH4 content, etc.) and isotopic (18O and D) composition of the Lago Fagnano watershed. These data are now integrated into an existing database of comparable chemical/physical information gathered for North American sites through our summer field courses. We will utilize this rich data set to make Texas-Tierra del Fuego ecosystem comparisons with our classes. The level of mentoring, preparation and follow-up provided by an NSF GK-12 Fellow was a key factor contributing to the success of our experience and an important element in helping us transfer components of this challenging experience to our students. Before, during, and following a two-week field season at Lago Fagnano, we and our students were actively engaged as learners and as scientists. We acquired concepts and skills that are readily applicable in a classroom setting: geologic mapping, GIS applications, isotopic data collection and analysis, tectonics concepts, and a general understanding of how science is truly conducted. Other factors that contributed to a positive experience included the team of dynamic scientists, who encouraged, helped and inspired us, the strong support that we received from our high school campus and district level

  13. Impact of glaciations on the long-term erosion in Southern Patagonian Andes

    NASA Astrophysics Data System (ADS)

    Simon-Labric, Thibaud; Herman, Frederic; Baumgartner, Lukas; Shuster, David L.; Braun, Jean; Reiners, Pete W.; Valla, Pierre G.; Leuthold, Julien

    2014-05-01

    The Southern Patagonian Andes are an ideal setting to study the impact of Late-Cenozoic climate cooling and onset of glaciations impact on the erosional history of mountain belts. The lack of tectonic activity during the last ~12 Myr makes the denudation history mainly controlled by surface processes, not by tectonics. Moreover, the glaciations history of Patagonia shows the best-preserved records within the southern hemisphere (with the exception of Antarctica). Indeed, the dry climate on the leeward side of Patagonia and the presence of lava flows interbedded with glacial deposits has allowed an exceptional preservation of late Cenozoic moraines with precise dating using K-Ar analyses on lava flow. The chronology of moraines reveals a long history covering all the Quaternary, Pliocene, and up to the Upper Miocene. The early growth of large glaciers flowing on eastern foothills started at ~7-6 Myr, while the maximum ice-sheet extent dates from approximately 1.1 Myr. In order to quantify the erosion history of the Southern Patagonian Andes and compare it to the glaciations sediment record, we collected samples along an age-elevation profile for low-temperature thermochronology in the eastern side of the mountain belt (Torres del Paine massif). The (U-Th)/He age-elevation relationship shows a clear convex shape providing an apparent long-term exhumation rate of ~0.2 km/Myr followed by an exhumation rate increase at ~6 Myr. Preliminary results of 4He/3He thermochronometry for a subset of samples complete the erosion history for the Plio-Pleistocene epoch. We used inverse procedure predicting 4He distributions within an apatite grain using a radiation-damage and annealing model to quantify He-diffusion kinetics in apatite. The model also allows quantifying the impact of potential U-Th zonation throughout each apatite crystal. Inversion results reveal a denudation history composed by a pulse of denudation at ~6 Ma, as suggested by the age-elevation relationship

  14. Geophysical modeling and structure of Ushuaia Pluton, Fuegian Andes, Argentina

    NASA Astrophysics Data System (ADS)

    Peroni, Javier Ignacio; Tassone, Alejandro Alberto; Menichetti, Marco; Cerredo, María Elena

    2009-10-01

    Within the area of Ushuaia Bay (Tierra del Fuego, southernmost South America) the deformed Lower Cretaceous sedimentary rocks of Yahgán Formation host the Ushuaia Pluton. The intrusive body is oval in map view; it is compositionally varied with rocks ranging from the ultrabasic to the mesosiliceous realm. The emplacement time is constrained within the Albian-Cenomanian span by new amphibole K/Ar data. Meso- and microstructures of Ushuaia Pluton and its host indicate a synkinematic emplacement with a dominant extensional component. A set of transcurrent and normal faults related to the sinistral strike-slip Beagle Channel Fault System affects the pluton and its host. On the basis of aeromagnetic data combined with field information, a new model is presented for the Ushuaia Pluton. Modeling results fit well with a laccolithic body with an estimated volume of around 111 km 3. The model pluton cross-section displays a central zone with an average thickness of 2000 m which progressively thins toward the margins (˜ 500 m) and a southern root which reaches 5000 m deep. The combined structural and geophysical model supports a transtensive scenario for the Ushuaia Pluton emplacement at Early-Late Cretaceous boundary.

  15. SIR-B radar imagery of volcanic deposits in the Andes

    NASA Technical Reports Server (NTRS)

    Fielding, E. J.; Knox, W. J., Jr.; Bloom, A. L.

    1986-01-01

    Synthetic-aperture radar imagery from the Shuttle Imaging Radar - mission B (SIR-B) was collected in October 1984 over the central Andes between 20 deg S and 24 deg S and also south of 42 deg S. Despite signal-strength problems that drastically reduced the signal-to-noise ratio of the images, volcanic features of both areas show up well. In particular, ignimbrite sheets formed by large explosive eruptions stand out as very strong radar reflectors. High backscatter is apparently caused by erosional relief on the ignimbrites at scales ranging from the radar wavelength (23 cm for SIR-B) to the 30-200-m scale of quebradas (gullies and canyons). The consistent regional erosional pattern appears unrelated to the emplacement of the ignimbrites, and is probably caused by preferential eolian erosion in the directions of the prevailing wind. Hand-held space photographs, ground observations, and Landsat Thematic Mapper imagery support the interpretation of the ignimbrite radar signature. The Chilean volcano Michinmahuida was imaged by four radar data takes at different incidence angles, which show tectonic, glacial, and volcanic features of that nearly inaccessible and often cloud-covered region. Stereo viewing of radar images from two data takes greatly enhances the geologic interpretation of this rugged area.

  16. Homogeneous temperature and precipitation series for a Peruvian High Andes regions from 1965 to 2009

    NASA Astrophysics Data System (ADS)

    Acuña, D.; Serpa Lopez, B.; Silvestre, E.; Konzelmann, Th.; Rohrer, M.; Schwarb, M.; Salzmann, N.

    2010-09-01

    As a basis of a joint Swiss-Peruvian effort focused on water resources, food security and disaster preparedness (Peruvian Climate Adaptation Project, PACC) clean and homogenized meteorological datasets have been elaborated for the Cusco and Apurimac Regions in the Central Andes. Operational and historical data series of more than 100 stations of the Peruvian Meteorological and Hydrological Service (SENAMHI) were available as a data base. Additionally, meteorological data provided by the National Climatic Data Centre (NCDC) or the Meteorological Aerodrome Records (METAR), have been considered. In contrast to many European countries, where most conventional sensors have been replaced by automated sensors during the last decades, instrumentation of climatological stations remained unchanged in Peru. Station records and station history of the Cusco-Apurimac-region are partially fragmentary or lost, mainly because of armed conflicts, particularly in the 1980ies. Moreover, many stations do observe precipitation as only variable. As a consequence, it was only possible so far to elaborate four complete homogenized air temperature series (Curahuasi 2763m a.s.l., Granja Kcayra-Cusco 3219m, Sicuani, 3574m and La Angostura, 4150m) since 1965. For precipitation a larger number of stations was available for elaboration, which is important because of the small scaled characteristics of the mostly convective type precipitation events in these regions. Based on these homogenized series, linear and gaussian low pass filtered trends have been calculated for all series of precipitation and air temperature records.

  17. Tectonic geomorphology of large normal faults bounding the Cuzco rift basin within the southern Peruvian Andes

    NASA Astrophysics Data System (ADS)

    Byers, C.; Mann, P.

    2015-12-01

    The Cuzco basin forms a 80-wide, relatively flat valley within the High Andes of southern Peru. This larger basin includes the regional capital of Cuzco and the Urubamba Valley, or "Sacred Valley of the Incas" favored by the Incas for its mild climate and broader expanses of less rugged and arable land. The valley is bounded on its northern edge by a 100-km-long and 10-km-wide zone of down-to-the-south systems of normal faults that separate the lower area of the down-dropped plateau of central Peru and the more elevated area of the Eastern Cordillera foldbelt that overthrusts the Amazon lowlands to the east. Previous workers have shown that the normal faults are dipslip with up to 600 m of measured displacements, reflect north-south extension, and have Holocene displacments with some linked to destructive, historical earthquakes. We have constructed topographic and structural cross sections across the entire area to demonstrate the normal fault on a the plateau peneplain. The footwall of the Eastern Cordillera, capped by snowcapped peaks in excess of 6 km, tilts a peneplain surface northward while the hanging wall of the Cuzco basin is radially arched. Erosion is accelerated along the trend of the normal fault zone. As the normal fault zone changes its strike from east-west to more more northwest-southeast, normal displacement decreases and is replaced by a left-lateral strike-slip component.

  18. Agriculture at the Edge: Landscape Variability of Soil C Stocks and Fluxes in the Tropical Andes

    NASA Astrophysics Data System (ADS)

    Riveros-Iregui, D. A.; Peña, C.

    2015-12-01

    Paramos, or tropical alpine grasslands occurring right above the forest tree-line (2,800 - 4,700 m), are among the most transformed landscapes in the humid tropics. In the Tropical Andes, Paramos form an archipelago-like pattern from Northern Colombia to Central Peru that effectively captures atmospheric moisture originated in the Amazon-Orinoco basins, while marking the highest altitude capable of sustaining vegetation growth (i.e., 'the edge'). This study investigates the role of land management on mediating soil carbon stocks and fluxes in Paramo ecosystems of the Eastern Cordillera of Colombia. Observations were collected at a Paramo site strongly modified by land use change, including active potato plantations, pasture, tillage, and land abandonment. Results show that undisturbed Paramos soils have high total organic carbon (TOC), high soil water content (SWC), and low soil CO2 efflux (RS) rates. However, Paramo soils that experience human intervention show lower TOC, higher and more variable RS rates, and lower SWC. This study demonstrates that changes in land use in Paramos affect differentially the accumulation and exchange of soil carbon with the atmosphere and offers implications for management and protection strategies of what has been deemed the fastest evolving biodiversity ecosystem in the world.

  19. The extended tracking network and indications of baseline precision and accuracy in the North Andes

    NASA Technical Reports Server (NTRS)

    Freymueller, Jeffrey T.; Kellogg, James N.

    1990-01-01

    The CASA Uno Global Positioning System (GPS) experiment (January-February 1988) included an extended tracking network which covered three continents in addition to the network of scientific interest in Central and South America. The repeatability of long baselines (400-1000 km) in South America is improved by up to a factor of two in the horizontal vector baseline components by using tracking stations in the Pacific and Europe to supplement stations in North America. In every case but one, the differences between the mean solutions obtained using different tracking networks was equal to or smaller than day-to-day rms repeatabilities for the same baselines. The mean solutions obtained by using tracking stations in North America and the Pacific agreed at the 2-3 millimeter level with those using tracking stations in North America and Europe. The agreement of the extended tracking network solutions suggests that a broad distribution of tracking stations provides better geometric constraints on the satellite orbits and that solutions are not sensitive to changes in tracking network configuration when an extended network is use. A comparison of the results from the North Andes and a baseline in North America suggests that the use of a geometrically strong extended tracking network is most important when the network of interest is far from North America.

  20. Rainfall variability and trends of the past six decades (1950-2014) in the subtropical NW Argentine Andes

    NASA Astrophysics Data System (ADS)

    Castino, F.; Bookhagen, B.; Strecker, M. R.

    2016-04-01

    The eastern flanks of the Central Andes are characterized by deep convection, exposing them to hydrometeorological extreme events, often resulting in floods and a variety of mass movements. We assessed the spatiotemporal pattern of rainfall trends and the changes in the magnitude and frequency of extreme events (≥95th percentile) along an E-W traverse across the southern Central Andes using rain-gauge and high-resolution gridded datasets (CPC-uni and TRMM 3B42 V7). We generated different climate indices and made three key observations: (1) an increase of the annual rainfall has occurred at the transition between low (<0.5 km) and intermediate (0.5-3 km) elevations between 1950 and 2014. Also, rainfall increases during the wet season and, to a lesser degree, decreases during the dry season. Increasing trends in annual total amounts characterize the period 1979-2014 in the arid, high-elevation southern Andean Plateau, whereas trend reversals with decreasing annual total amounts were found at low elevations. (2) For all analyzed periods, we observed small or no changes in the median values of the rainfall-frequency distribution, but significant trends with intensification or attenuation in the 95th percentile. (3) In the southern Andean Plateau, extreme rainfall events exhibit trends towards increasing magnitude and, to a lesser degree, frequency during the wet season, at least since 1979. Our analysis revealed that low (<0.5 km), intermediate (0.5-3 km), and high-elevation (>3 km) areas respond differently to changing climate conditions, and the transition zone between low and intermediate elevations is characterized by the most significant changes.

  1. Diatom Assemblages on Lacustrine Sediments from the Tropical Andes, Southern Peru: Modern Analogs for Ancient Environments

    NASA Astrophysics Data System (ADS)

    Tapia, P. M.; Vargas, J.; Beal, S. A.; Stroup, J. S.; Kelly, M. A.

    2012-12-01

    Diatom analysis of surface sediments from 17 high-altitude lakes (~3,100-5,000 m asl) in the Cuzco area, Peru, reveals several potential environmental settings that have been observed in biostratigraphy records from lakes in the tropical Andes. The sedimentation rates in several lakes from this area range between 1 and 1.6 mm yr-1 during the late Quaternary, thus we assume our surface samples represent conditions spanning from 6 to 10 years for the top 1cm. Physical and chemical analysis show a high variability in water depth (0.5-12.3 m), pH (7.5-9.7), temperature (4.6-16.5 °C) and conductivity (5.6-3205 μS cm -1), as well as cationic (Na+, K+, Mg2+, Ca2+, Al3+, Mn3+, Fe3+) and anionic (F-, Cl-, Br-, SO42-) composition. Most of the lakes were oligotrophic (PO43-and NO32- below limit of detection) with the exception of nitrite. Principle Component Analysis suggests that the sites follows a strong gradient in conductivity + anions & cations (Axis 1, explaining 51.61 % of variance), and pH + water depth (Axis 2, 17.36 %). Diatoms are quite abundant (108-1010 valves g dry sed-1) in these samples, indicating oligotrophic to mesotrophic conditions and fresh to brackish waters, sometimes forming almost monospecific associations. Applications of these assemblages may be found in the Lake Junin, Central Peruvian Andes. The high abundance (92%) of the pennate diatom Denticula elegans from Site PLS-9 is similar at the Junin Biozone JU-3 that covers most of the Holocene. This species prospers in shallow (1.3-m), high conductivity (3205 μS cm-1) and alkaline (pH 9.39) waters with high values in Ca, Mg and sulfate. Similarly, the dominance (95%) of the centric diatom Discotella stelligera at Site PLS-8 resemble Biozone JU-2, ~17,000 cal yr BP, with deeper (10.9 m), lower conductivity (48.8 μS cm-1) and slightly-alkaline (pH 7.82) waters, with at least 2 orders of magnitude lower in chemical parameters than Site PLS-9. These findings encourage the survey of additional modern

  2. Tectonostratigraphic reconstruction Cretaceous volcano-sedimentary in the northwestern Andes: from extensional tectonics to arc accretion.

    NASA Astrophysics Data System (ADS)

    Zapata, S.; Patino, A. M.; Cardona, A.; Mejia, D.; Leon, S.; Jaramillo, J. S.; Valencia, V.; Parra, M.; Hincapie, S.

    2014-12-01

    Active continental margins characterized by continuous convergence experienced overimposed tectonic configurations that allowed the formation of volcanic arcs, back arc basins, transtensional divergent tectonics or the accretion of exotic volcanic terranes. Such record, particularly the extensional phases, can be partially destroyed and obscure by multiple deformational events, the accretion of exotic terranes and strike slip fragmentation along the margin. The tectonic evolution of the northern Andes during the Mesozoic is the result of post Pangea extension followed by the installation of a long-lived Jurassic volcanic arc (209 - 136 ma) that apparently stops between 136 Ma and 110 Ma. The Quebradagrande Complex has been define as a single Lower Cretaceous volcano-sedimentary unit exposed in the western flank of the Central Cordillera of the Colombian Andes that growth after the Late Jurassic to Early Cretaceous magmatic hiatus. The origin of this unit have been related either to an oceanic volcanic arc or a marginal basin environment. The existence of such contrasting models reflect the regional perspective followed in published studies and the paucity of detail analysis of the volcano-sedimentary sequences.We integrate multiple approaches including structural mapping, stratigraphy, geochemistry, U-Pb provenance and geochronology to improve the understanding of this unit and track the earlier phases of accumulation that are mask on the overimposed tectonic history. Our preliminary results suggest the existence of different volcano-sedimentary units that accumulated between 100 Ma and 82 Ma.The older Lower Cretaceous sequences was deposited over Triassic metamorphic continental crust and include a upward basin deepening record characterized by thick fan delta conglomerates, followed by distal turbidites and a syn-sedimentary volcanic record at 100 ma. The other sequence include a 85 - 82 Ma fringing arc that was also formed close to the continental margin or

  3. The Basement of the Andes: the Gondwana-Laurentia Connections Revisited

    NASA Astrophysics Data System (ADS)

    Ramos, V. A.

    2009-05-01

    The research performed in the last decade in the basement of the Andes have shown that the Precambrian and Paleozoic rocks have recorded a series of igneous and metamorphic events through time. These episodes can be grouped in discrete orogenic events, which have different paleogeographic distribution and intensity. The first and most important orogenic event is widely distributed along the margin and correspond to the Sunsas-Grenville orogen. Evidence of metamorphism and associated magmatic rocks are found from Colombia to the southernmost Patagonia. This episode produced the amalgamation of Amazonia, Pampia and Patagonia, among other cratonic blocks, to form Rodinia. The Rodinia break-up leaved several cratonic blocks accreted in the Gondwana side, such as Marañón, Arequipa, and Antofalla, although the generalized extension of this period produced crustal attenuation, rifted basins, and limited oceanic realms during late Proterozoic times. The Brasiliano-Pampean orogeny reamalgamated these blocks against the Gondwana margin. A new episode of break-up produced the dispersal of several Gondwanian blocks, separation along some previous sutures, crustal attenuation and magmatism in Late Cambrian times, until the new amalgamation occurred in Middle Late Ordovician times. These processes led to the Famatinian orogeny when metamorphism and arc magmatism was widely spread along the continental margin, as seen in Chibcha, Marañón, Arequipa and Sierras Pampeanas. Besides the re-accretion of some parautochthonous terranes, new exotic blocks were derived from Laurentia, such as the Cuyania terrane, which finally collided against the Andean proto-margin at ~ 460 Ma to form the Argentine Precordillera and surrounding regions. Late accretion in Early to Middle Devonian times of Chilenia and related terranes formed most of the basement of Central Andes. Final collision between Laurentia and Gondwana in the Late Carboniferous - Early Permian times to form the Alleghanides

  4. Late Cretaceous-early Eocene counterclockwise rotation of the Fueguian Andes and evolution of the Patagonia-Antarctic Peninsula system

    NASA Astrophysics Data System (ADS)

    Poblete, F.; Roperch, P.; Arriagada, C.; Ruffet, G.; Ramírez de Arellano, C.; Hervé, F.; Poujol, M.

    2016-02-01

    The southernmost Andes of Patagonia and Tierra del Fuego present a prominent arc-shaped structure: the Patagonian Bend. Whether the bending is a primary curvature or an orocline is still matter of controversy. New paleomagnetic data have been obtained south of the Beagle Channel in 39 out of 61 sites. They have been drilled in Late Jurassic and Early Cretaceous sediments and interbedded volcanics and in mid-Cretaceous to Eocene intrusives of the Fuegian Batholith. The anisotropy of magnetic susceptibility was measured at each site and the influence of magnetic fabric on the characteristic remanent magnetizations (ChRM) in plutonic rocks was corrected using inverse tensors of anisotropy of remanent magnetizations. Normal polarity secondary magnetizations with west-directed declination were obtained in the sediments and they did not pass the fold test. These characteristic directions are similar to those recorded by mid Cretaceous intrusives suggesting a remagnetization event during the normal Cretaceous superchron and describe a large (> 90°) counterclockwise rotation. Late Cretaceous to Eocene rocks of the Fueguian Batholith, record decreasing counterclockwise rotations of 45° to 30°. These paleomagnetic results are interpreted as evidence of a large counterclockwise rotation of the Fueguian Andes related to the closure of the Rocas Verdes Basin and the formation of the Darwin Cordillera during the Late Cretaceous and Paleocene. The tectonic evolution of the Patagonian Bend can thus be described as the formation of a progressive arc from an oroclinal stage during the closure of the Rocas Verdes basin to a mainly primary arc during the final stages of deformation of the Magallanes fold and thrust belt. Plate reconstructions show that the Antarctic Peninsula would have formed a continuous margin with Patagonia between the Early Cretaceous and the Eocene, and acted as a non-rotational rigid block facilitating the development of the Patagonian Bend.

  5. CENOZOIC EXHUMATION OF THE ANTIOQUEÑO PLATEAU, NORTHERN ANDES, COLOMBIA, FROM APATITE LOW-TEMPERATURE THERMOCHRONOLOGY

    NASA Astrophysics Data System (ADS)

    Restrepo-Moreno, S. A.; Foster, D. A.; O'Sullivan, P. B.; Donelick, R.; Stockli, D. F.

    2009-12-01

    The Antioqueño plateau (AP), in the northernmost Cordillera Central, Colombia, is the most extensive and best preserved relict surface in the Northern Andes. Apatite (U-Th)/He (AHe) and fission track (AFT) results from twenty two samples, collected from paleocrustal depths along two vertical profiles in canyons dissecting the AP, constrain Cenozoic erosional exhumation of this segment of the Andean range. The two profiles exhibit excellent reproducibility of AHe and AFT data. Helium ages increase with elevation from ~22-49 Ma. A marked inflection point in the AHe age-elevation plots at 25 Ma defines the bottom of the post-Oligocene He partial retention zone (PRZ). Virtually invariant ages at ~25 Ma record onset of rapid exhumation in the AP. A more subtle slope change in the PRZ at ~43 Ma is interpreted as a minor exhumation pulse. AFT better defines timing and intensity of Eocene exhumation. AFT ages for both profiles vary from ~30-49 Ma and are consistently older than AHe ages. AFT data display invariant ages (±2σ) between 1500-2400 m elevations while confined track length data exhibit uni-modal distributions with a mean track length of ~14.2 μm. Both facts indicate rapid cooling. This is further supported by virtually concordant AFT and AHe ages for both profiles between 1500 to 2200 m implying that rocks were exhumed from temperatures >120°C to below AHe closure temperature 60°C. Assuming a geothermal gradient of ~25°C/km this corresponds to exhumation rates in the order of 0.5 mm/y, comparable in intensity to the Miocene pulse defined by AHe. Integrated thermal modeling show an episode of rapid cooling at ~43-49 Ma. AFT profiles show an apparent inflection point at ~1400 m, which defines the upper boundary of an apatite partial annealing zone (PAZ) exhumed during the 43-49 Ma cooling event. The position of the PAZ and PRZ relative to the present erosional surface point to average erosion rates of ~0.03 mm/yr, which constitute very low denudation rates

  6. Multiproxy Holocene paleoclimate records from the southern Peruvian Andes - what new can we learn from the stable carbon isotope composition of high altitude organic matter deposits?

    NASA Astrophysics Data System (ADS)

    Skrzypek, Grzegorz; Engel, Zbyněk

    2015-04-01

    Interpretation of the Central Andean paleoclimate over the last millennia still represents a research challenge demanding deeper studies [1,2]. Several high-resolution paleoclimate proxies for the last 10,000 years have been developed for the northern hemisphere. However, similar proxies are very limited for South America, particularly for high altitudes where, for example, tree-ring chronologies are not available and instrumental records are very limited. Consequently, our knowledge of high altitude climate changes in arid regions of the Peruvian Andes mainly relies on ice-core and lake deposit studies. In our study, we used a new alternative proxy for interpretation of palaeoclimate conditions based on a peat core taken from the Carhuasanta Valley at the foot of Nevado Mismi in the southern Peruvian Andes (15° 30'S, 71° 43'W, 4809m a.s.l.). The stable carbon isotope composition (δ13C) of Distichia peat reflects mainly the relative variation of the mean air temperature during subsequent growing seasons [3], and allows reconstructions of palaeotemperature changes. In contrast, peat organic carbon concentration (C % wt) records mainly wetness in the valley, directly corresponding to the changes in runoff in the upper part of the catchment. The most prominent climate changes recorded in the peat over last 4ka occurred between 3040 and 2750 cal. yrs BP. The initial warming turned to a very rapid cooling to temperatures at least 2° C lower than the mean for the Late Holocene. Initially drier conditions within this event turned to a short wet phase after 2780 cal. yrs BP, when the temperature increased again. This event coincides with significant changes in peat and ice core records in the Central Andes that match the timing of the global climate event around 2.8 cal. ka BP. Climatic conditions in the study area became relatively dry and stable after the event for about 800 years. Highly variable temperatures and humidity prevailed during the last 2000 years, when

  7. Geochemical and thermochronological signals in Tertiary to Recent sediments from the Western Andes (15-19°S): proxies for sediment provenance and Andean uplift.

    NASA Astrophysics Data System (ADS)

    Decou, A.; Mamani, M.; von Eynatten, H.; Wörner, G.

    2009-04-01

    During the Cenozoic the landscape at the western margin of South America changed dramatically due to the tectonic evolution of the Andes (Isacks 1988, J Geophysical Res 93) and significant variations in climate (Gregory-Wodzicki 2000, GSA Bulletin 112). At present day the climate in the western Central Andes (N-Chile, S-Peru) is arid (rainfall average is less than 100-200 mm/y) Climate has changed significantly through time, for example, sediments on the Altiplano and the eastern Central Andes indicate a period of increased precipitation at around 7-8 Ma (Gaupp et al. 1999, PPP 151; Uba et al. 2007, Geology 35). The uplift of the Andes started some 30-25 My ago (Isacks, 1988,). Siliciclastic sedimentation along the western flank of the Central Andes started at 55 Ma and lasted until recent time (Moquegua Group, Roperch et al. 2006, Tectonics 25). This implies that a river system with sediment deposition was already developed before the Andean uplift which occurred during deposition of the Moquegua Group. The Moquegua group is composed of four units: Moquegua A (55-45Ma), Moquegua B (45-30Ma), Moquegua C (30-15?Ma) and Moquegua D (15?-0Ma) (Roperch et al. 2006). The sedimentary basin of Moquegua has a complex internal structure and is composed of different subbasins. We focus in this study respectively, from north to south, on the Cuno Cuno section (cut by the Rio Ocoña), the Majes section (cut by the Rio Majes) and the Moquegua section (cut by the Rio Moquegua). Several facies and compositional changes of Moquegua Group sediments, both along orogenic strike and through time, are already described; however, it lacks a detailed provenance study to constrain the tectonic and climatic controls on sediment generation, dispersal, and accumulation. To do so sandstones from all Moquegua units from the three different sections have been sampled. Because it is crucial to know all the potential source rocks in some detail, the Proterozoic-Paleozoic basement, the Jurassic

  8. Person-to-Person Transmission of Andes Virus

    PubMed Central

    Bellomo, Carla; San Juan, Jorge; Pinna, Diego; Forlenza, Raul; Elder, Malco; Padula, Paula J.

    2005-01-01

    Despite the fact that rodents are considered to be the infectious source of hantavirus for humans, another route of transmission was demonstrated. Andes virus (ANDV) has been responsible for most of the cases recorded in Argentina. Person-to-person transmission of ANDV Sout lineage was described during an outbreak of hantavirus pulmonary syndrome in southwest Argentina. In this study, we analyzed 4 clusters that occurred in 2 disease-endemic areas for different ANDV lineages. We found new evidence of interhuman transmission for ANDV Sout lineage and described the first event in which another lineage, ANDV Cent BsAs, was implicated in this mechanism of transmission. On the basis of epidemiologic and genetic data, we concluded that person-to-person spread of the virus likely took place during the prodromal phase or shortly after it ended, since close and prolonged contact occurred in the events analyzed here, and the incubation period was 15–24 days. PMID:16485469

  9. Early local last glacial maximum in the tropical Andes.

    PubMed

    Smith, Jacqueline A; Seltzer, Geoffrey O; Farber, Daniel L; Rodbell, Donald T; Finkel, Robert C

    2005-04-29

    The local last glacial maximum in the tropical Andes was earlier and less extensive than previously thought, based on 106 cosmogenic ages (from beryllium-10 dating) from moraines in Peru and Bolivia. Glaciers reached their greatest extent in the last glacial cycle approximately 34,000 years before the present and were retreating by approximately 21,000 years before the present, implying that tropical controls on ice volumes were asynchronous with those in the Northern Hemisphere. Our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures, which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle. PMID:15860623

  10. Paleoindian settlement of the high-altitude Peruvian Andes.

    PubMed

    Rademaker, Kurt; Hodgins, Gregory; Moore, Katherine; Zarrillo, Sonia; Miller, Christopher; Bromley, Gordon R M; Leach, Peter; Reid, David A; Álvarez, Willy Yépez; Sandweiss, Daniel H

    2014-10-24

    Study of human adaptation to extreme environments is important for understanding our cultural and genetic capacity for survival. The Pucuncho Basin in the southern Peruvian Andes contains the highest-altitude Pleistocene archaeological sites yet identified in the world, about 900 meters above confidently dated contemporary sites. The Pucuncho workshop site [4355 meters above sea level (masl)] includes two fishtail projectile points, which date to about 12.8 to 11.5 thousand years ago (ka). Cuncaicha rock shelter (4480 masl) has a robust, well-preserved, and well-dated occupation sequence spanning the past 12.4 thousand years (ky), with 21 dates older than 11.5 ka. Our results demonstrate that despite cold temperatures and low-oxygen conditions, hunter-gatherers colonized extreme high-altitude Andean environments in the Terminal Pleistocene, within about 2 ky of the initial entry of humans to South America. PMID:25342802

  11. Complex brittle deformation pattern along the Southern Patagonian Andes (Argentina)

    NASA Astrophysics Data System (ADS)

    Barberón, Vanesa; Sue, Christian; Ronda, Gonzalo; Ghiglione, Matías

    2016-04-01

    The Southern Patagonian Andes is located in the southern extreme of the Pacific subduction zone, where the Antartic oceanic plate sinks underneath South America. The history of the area begins with compression during Paleozoic, Jurassic extension associated to the rift and opening of the South Atlantic Ocean, then a sag stage in the Lower Cretaceous followed by a foreland phase as a result of plate tectonics (Ghiglione et al., 2016). The kinematic study is concentrated in the Argentinean foothills, between 46°40' and 48° SL. We measured around 800 fault planes and their striaes with the sense of movement in order to characterize the stress field. The software used to make the stress inversion were Tensor (Delvaux, 2011) and Multiple Inverse Method MIM (Yamaji et al., 2011). The stress field map was built with the results of the MIM. We present new data from 48 sites located in the northern sector of the Southern Patagonian Andes. The measurements were made in several rocks from Paleozoic to Lower Cretaceous, even though most were taken in pyroclastic jurassic rocks from El Quemado Complex. Paleostress tensors obtained are mostly strike-slip, although a 25% is normal and there are a few compresional. The pattern of faults found is complex. In some sites the tensor can be locally linked to satellite images and observations from the field or be related to a major thrust front. There is no clear correlation between the age and/or lithology with the tensor since the youngest rocks measured are Lower Cretaceous. Probably there are several generations of family faults connected to different and recent tectonic phases then the paleostress tensors might correspond to the latest tectonic events.

  12. Deglaciation and Holocene climate change in the western Peruvian Andes

    NASA Astrophysics Data System (ADS)

    Weng, Chengyu; Bush, Mark B.; Curtis, Jason H.; Kolata, Alan L.; Dillehay, Tom D.; Binford, Michael W.

    2006-07-01

    Pollen, charcoal, magnetic susceptibility, and bulk density data provide the first paleoecological record spanning the last 33,000 years from the western cordillera of the Peruvian Andes. Sparse super-puna vegetation existed before 30,000 cal yr B.P. around Lake Compuerta (3950 m elevation), prior to a sedimentary hiatus that lasted until c. 16,200 cal yr B.P. When sedimentation resumed, a glacial foreland or super-puna flora is represented in which Polylepis was a significant element. Glacial outwash, marked by high sedimentary magnetic susceptibility, increased from c.16,200 cal yr B.P. and reached a peak at c. 13,200 cal yr B.P. Between c. 12,500 cal yr B.P. and 10,000 cal yr B.P., magnetic susceptibility was reduced. Vegetation shifts suggest a cool dry time, consistent with regional descriptions of the Younger Dryas event. Deglaciation resumes by 10,000 cal yr B.P. and the last ice is lost from the catchment at ˜7500 cal yr B.P. During the early Holocene warm and dry period between 10,000 and 5500 cal yr B.P., Alnus expanded in downslope forests. Alnus declined in abundance at 5500 cal yr B.P. when wetter and cooler conditions returned and human activity intensified. Maize ( Zea mays) pollen first occurred in the core at ˜2600 cal yr B.P., indicating a minimum age for local agriculture. An increase in Alnus pollen abundance at ˜1000 cal yr B.P. could be due to human activity or perhaps due to a regional climate change associated with cultural turnover elsewhere in the Andes at this time.

  13. PROTOPLANETARY DISK STRUCTURE WITH GRAIN EVOLUTION: THE ANDES MODEL

    SciTech Connect

    Akimkin, V.; Wiebe, D.; Pavlyuchenkov, Ya.; Zhukovska, S.; Semenov, D.; Henning, Th.; Vasyunin, A.; Birnstiel, T. E-mail: dwiebe@inasan.ru E-mail: zhukovska@mpia.de E-mail: henning@mpia.de E-mail: tbirnstiel@cfa.harvard.edu

    2013-03-20

    We present a self-consistent model of a protoplanetary disk: 'ANDES' ('AccretioN disk with Dust Evolution and Sedimentation'). ANDES is based on a flexible and extendable modular structure that includes (1) a 1+1D frequency-dependent continuum radiative transfer module, (2) a module to calculate the chemical evolution using an extended gas-grain network with UV/X-ray-driven processes and surface reactions, (3) a module to calculate the gas thermal energy balance, and (4) a 1+1D module that simulates dust grain evolution. For the first time, grain evolution and time-dependent molecular chemistry are included in a protoplanetary disk model. We find that grain growth and sedimentation of large grains onto the disk midplane lead to a dust-depleted atmosphere. Consequently, dust and gas temperatures become higher in the inner disk (R {approx}< 50 AU) and lower in the outer disk (R {approx}> 50 AU), in comparison with the disk model with pristine dust. The response of disk chemical structure to the dust growth and sedimentation is twofold. First, due to higher transparency a partly UV-shielded molecular layer is shifted closer to the dense midplane. Second, the presence of big grains in the disk midplane delays the freeze-out of volatile gas-phase species such as CO there, while in adjacent upper layers the depletion is still effective. Molecular concentrations and thus column densities of many species are enhanced in the disk model with dust evolution, e.g., CO{sub 2}, NH{sub 2}CN, HNO, H{sub 2}O, HCOOH, HCN, and CO. We also show that time-dependent chemistry is important for a proper description of gas thermal balance.

  14. Geochronologic and paleontologic evidence for a Pacific-Atlantic connection during the late Oligocene-early Miocene in the Patagonian Andes (43-44°S)

    NASA Astrophysics Data System (ADS)

    Encinas, Alfonso; Pérez, Felipe; Nielsen, Sven N.; Finger, Kenneth L.; Valencia, Victor; Duhart, Paul

    2014-11-01

    Cenozoic marine strata occur in the western, eastern, and central parts of the North Patagonian Andes between ˜43°S and 44°S. Correlation of these deposits is difficult because they occur in small and discontinuous outcrops and their ages are uncertain. In order to better understand the age and sedimentary environment of these strata, we combined U-Pb (LA-MC-ICPMS) geochronology on detrital zircons with sedimentologic and paleontologic (foraminifers and molluscs) studies. Sedimentologic analyses suggest that the Puduhuapi Formation on the western flank of the Andean Cordillera was deposited in a deep-marine setting, the Vargas Formation in the central part of the Andes was deposited at outer-neritic or bathyal depths, and the La Cascada Formation on the eastern flank of the range was deposited in a shallow-marine environment. Geochronologic and paleontologic results indicate that the three marine units were deposited during the late Oligocene-early Miocene interval, although it is not clear whether this occurred during one or more marine incursions in the area. The alluvial(?) conglomeratic deposits of the La Junta Formation, exposed in the proximity of the Vargas Formation outcrops, have a maximum depositional age of ˜26 Ma and could have been deposited during the initial stage of subsidence that affected this region prior to the marine transgression over this area. The occurrence of both Pacific and Atlantic molluscan taxa in the La Cascada and Vargas formations suggests that a marine strait connected both oceans during the accumulation of these units. The new data on the age of the Puduhuapi, Vargas, and La Cascada formations indicate that these units may correlate with lower Miocene marine deposits in the forearc of central and southern Chile (Navidad Formation and equivalent units) and on the eastern flank of the Patagonian Andes (Río Foyel Formation and equivalent units). A late Oligocene-early Miocene age for these marine deposits is a reliable maximum

  15. Investigating gravity waves and mesospheric temperature variability over the Andes Mountains

    NASA Astrophysics Data System (ADS)

    Taylor, M. J.; Pautet, P.; Zhao, Y.; Pugmire, J.; Criddle, N.; Swenson, G. R.; Liu, A. Z.; Hecht, J. H.

    2011-12-01

    The Andes region provides an excellent natural laboratory for investigating gravity wave influences on the Upper Mesospheric and Lower Thermospheric (MLT) dynamics with dominant gravity wave forcing expected from deep convection during the summer months replaced by strong orographic forcing during the wintertime, due to intense prevailing zonal winds blowing over the towering Andes mountain range. The instrument suite that comprised the very successful Maui-MALT program (2000-2005) was relocated to a new Andes Lidar Observatory (ALO) located high in the Andes mountains (2,520 m) at Cerro Pachon, Chile (30.3°S, 70.7°W). As part of this instrument set the Utah State University (USU) Mesospheric Temperature Mapper (MTM) has operated continuously over the past two years (August 2009-to date) measuring the nocturnal near infrared OH(6,2) band and the O2(0,1) Atmospheric band intensity and temperature perturbations to investigate a broad range of mesospheric wave forcings, their seasonal variability and effects on the MLT environment over the Andes. This presentation focuses on the strong variability observed from this site using collaborative investigations of selected wave events, including exceptionally large tidal perturbations (70-100 K), unusual "jumps" in OH/O2 temperature possibly associated with wave breaking, mesospheric bore events, and new evidence for quasi-stationary gravity waves, all illustrating the strong wave activity and its diversity over the Andes.

  16. Abundance and Morphological Effects of Large Woody Debris in Forested Basins of Southern Andes

    NASA Astrophysics Data System (ADS)

    Andreoli, A.; Comiti, F.; Lenzi, M. A.

    2006-12-01

    The Southern Andes mountain range represents an ideal location for studying large woody debris (LWD) in streams draining forested basins thanks to the presence of both pristine and managed woodland, and to the general low level of human alteration of stream corridors. However, no published investigations have been performed so far in such a large region. The investigated sites of this research are three basins (9-13 km2 drainage area, third-order channels) covered by Nothofagus forests: two of them are located in the Southern Chilean Andes (the Tres Arroyos in the Malalcahuello National Reserve and the Rio Toro within the Malleco Natural Reserve) and one basin lies in the Argentinean Tierra del Fuego (the Buena Esperanza basin, near the city of Ushuaia). Measured LWD were all wood pieces larger than 10 cm in diameter and 1 m in length, both in the active channel and in the adjacent active floodplain. Pieces forming log jams were all measured and the geometrical dimensions of jams were taken. Jam type was defined based on Abbe and Montgomery (2003) classification. Sediment stored behind log-steps and valley jams was evaluated approximating the sediment accumulated to a solid wedge whose geometrical dimensions were measured. Additional information relative to each LWD piece were recorded during the field survey: type (log, rootwad, log with rootwads attached), orientation to flow, origin (floated, bank erosion, landslide, natural mortality, harvest residuals) and position (log-step, in-channel, channel-bridging, channel margins, bankfull edge). In the Tres Arroyos, the average LWD volume stored within the bankfull channel is 710 m3 ha-1. The average number of pieces is 1,004 per hectare of bankfull channel area. Log-steps represent about 22% of all steps, whereas the elevation loss due to LWD (log-steps and valley jams) results in 27% loss of the total stream potential energy. About 1,600 m3 of sediment (assuming a porosity of 20%) is stored in the main channel

  17. Cooling and Exhumation of the Coastal Batholith in the Peruvian Andes (5-12°S)

    NASA Astrophysics Data System (ADS)

    Michalak, M.; Hall, S. R.; Farber, D.; Hourigan, J. K.; Audin, L.

    2014-12-01

    The South American Andes exhibit strong morphological differences along strike, shaped by a combination of tectonic forces and surface processes. In the central Peruvian Andes (~12°S) a major morphological transition occurs; to the north, the spines of the Western and Eastern Cordilleras come together into a relatively narrow configuration of high topography. In Southern Peru, the region of high topography widens, where the Western and Eastern Cordilleras flank the broad, Altiplano plateau. Despite this morphological change, the Mesozoic-early Cenozoic Coastal Batholith outcrops continuously from 0°-18°S along the western margin of the Peruvian Andes, emplaced along a trench-parallel marginal basin in the Mesozoic. The Coastal Batholith is an ideal geologic setting to investigate potential differences in rock exhumation and cooling histories along the western margin of Peru. While the cooling history of the southern Coastal Batholith has been previously used to estimate timing and magnitude of rock exhumation in Southern Peru, north of 12°S it is poorly constrained. We present 16 zircon and 7 apatite (U-Th)/He mean-ages from three sites, across seven degrees of latitude (5°S to 12°S). In general, ZHe and AHe ages capture two stages of cooling, Oligocene-to-mid-Miocene and mid-to-late Miocene, respectively. We model time-temperature histories of samples with paired AHe and ZHe ages using a Monte-Carlo inversion of HeFTy® (Ketcham, 2005); best fit time-temperature pathways show cooling rates ranging from ~2-24°C/my, where fastest cooling rates are generally observed in the mid-Miocene. To estimate exhumation rates, we apply a simple thermal model to account for nonuniform geothermal gradients expected in a trench-arc setting. Exhumation rates range from ~0.2mm/yr in the north, to 0.4-0.7mm/yr in the south, and rates increase orogenward, where mean elevation is highest. These results, particularly the predominance of Miocene ZHe and AHe data, and the younging

  18. Glacial Chronologies Along the Andes (30-40°S) and the Role of the Westerlies

    NASA Astrophysics Data System (ADS)

    Zech, R.; Eisenhut, A.; Kubik, P. W.; Veit, H.

    2008-12-01

    In arid and semi-arid mountain areas, like e.g the Central Andes, glaciers are moisture limited and thus more sensitive to precipitation changes rather than temperature changes. Glacial chronologies from such regions can therefore be out-of-phase with global temperature records, and reflect past changes in precipitation and related atmospheric circulation patterns, respectively. We have applied 10Be surface exposure dating at several locations along the Andes in order to establish glacial chronologies and to compare those with other paleoclimate proxies. At ~30°S, in the Valle Encierro and in the Cordon de Dona Rosa, pronounced moraines could be dated to between ~16 and 13 ka. Although today most precipitation at both locations occurs during austral winter and is related to the seasonal northward shift of the westerlies, we suggest that the Lateglacial advances at 30°S reflect the intensification and/or southward shift of the tropical circulation, which is well documented in numerous other records. An earlier, more extensive glacial advance at 30°S is dated to ~39 ka. This roughly coincides with the maximum glaciation that we dated in the Valle Rucachoroi at ~39°S (Argentina), and with 14C dated glacial advances in the northern Chilean Lake District (~40°S). We suggest that the westerlies were the moisture source for this "early local glacial maximum", and that the westerlies did not provide sufficient moisture north of ~39°S to allow for maximum glacial advances in-phase with the global temperature minimum during MIS 2. We will also present new exposure ages from moraines near Bariloche (Argentina, ~41°S) and from the Cerro Fredes (Chile, ~31.4°S), which provide minimum estimates of ~100 and 130 ka, respectively, for preserved older glacial deposits.

  19. The influence of topography on vertical velocity of air in relation to severe storms near the Southern Andes Mountains

    NASA Astrophysics Data System (ADS)

    de la Torre, A.; Pessano, H.; Hierro, R.; Santos, J. R.; Llamedo, P.; Alexander, P.

    2015-04-01

    On the basis of 180 storms which took place between 2004 and 2011 over the province of Mendoza (Argentina) near to the Andes Range at southern mid-latitudes, we consider those registered in the northern and central crop areas (oases). The regions affected by these storms are currently protected by an operational hail mitigation project. Differences with previously reported storms detected in the southern oasis are highlighted. Mendoza is a semiarid region situated roughly between 32S and 37S at the east of the highest Andes top. It forms a natural laboratory where different sources of gravity waves, mainly mountain waves, occur. In this work, we analyze the effects of flow over topography generating mountain waves and favoring deep convection. The joint occurrence of storms with hail production and mountain waves is determined from mesoscale numerical simulations, radar and radiosounding data. In particular, two case studies that properly represent diverse structures observed in the region are considered in detail. A continuous wavelet transform is applied to each variable and profile to detect the main oscillation modes present. Simulated temperature profiles are validated and compared with radiosounding data. Each first radar echo, time and location are determined. The necessary energy to lift a parcel to its level of free convection is tested from the Convective Available Potential Energy and Convection Inhibition. This last parameter is compared against the mountain waves' vertical kinetic energy. The time evolution and vertical structure of vertical velocity and equivalent potential temperature suggest in both cases that the detected mountain wave amplitudes are able to provide the necessary energy to lift the air parcel and trigger convection. A simple conceptual scheme linking the dynamical factors taking place before and during storm development is proposed.

  20. Late Pleistocene to Holocene tephrostratigraphy of the Lonquimay Volcano, South Central Chile

    NASA Astrophysics Data System (ADS)

    Gilbert, D.; Freundt, A.; Kutterolf, S.; Burkert, C.

    2010-12-01

    The Lonquimay Volcanic Complex (LVC) in South Central Chile (38.38°S, 71.58°W) is part of the Southern Volcanic Zone of the Andes, which formed in response to the subduction of the Nazca Plate beneath the South American Plate. During the course of its magmatic evolution, the LVC produced explosive eruptions documented in the succession of widespread tephra deposits, as well as large lava flows that originated from the main edifice and several adjacent minor eruptive centers. The last eruptive phase in Lonquimays volcanic evolution occurred from 1988-1990. It led to the formation of the Navidad cinder cone with its associated 10.2 km long lava flow, and a widely distributed tephra blanket of andesitic composition (Moreno and Gardeweg, 1989). During recent field work we reinvestigated and complemented the LVC tephrostratigraphy as originally established by Polanco (1998)by detailed logging of 22 outcrops and collecting 126 stratigraphically controlled samples that were analyzed for their matrix glass, mineral and bulk rock compositions. This data set allows us to verify and extend the field-based correlations, and to establish a tephrostratigraphy for the LVC that comprises 15 stratigraphic units (LQA-LQO) and provides a framework for ongoing investigations of the petrogenetic evolution of the LVC. The stratigraphic record identifies at least 13 explosive eruptions of VEI > 3 that occurred since the last glaciation period (17150 a BP, McCulloch et al. 2000). Magmatic compositions of the tephra deposits range from basaltic scoriae (51wt% SiO2) to evolved dacitic pumice lapilli layers (67wt% SiO2), and thus have a wider compositional range than the chemically distinct andesitic lavas (57-63wt%) of the LVC. The vertical succession of tephra compositions reflects four periods of progressive magmatic differentiation, each successively tapped by several eruptions. The maximum degree of fractionation reached during these periods increases to younger ages. The

  1. On recent measurements from the Andes Lidar Observatory

    NASA Astrophysics Data System (ADS)

    Liu, Alan Z.; Snively, Jonathan; Heale, Christopher; Cao, Bing

    2016-07-01

    The Andes Lidar Observatory is an upper atmosphere observatory located in Cerro Pachón, Chile (30.3S, 70.7W). It houses a Na Wind/Temperature Lidar, an all sky airglow imager, a mesospheric temperature mapper, an infrared imager and a meteor radar. This suite of instrumentation provides comprehensive measurements of the mesopause region and enables detailed study of wave dynamics. With the recent upgrade of the Na lidar, many complex dynamic processes were observed and resolved in detail. I will present several intriguing phenomena seen in the lidar measurement from recent campaigns, and a detailed analysis of a complex wave propagation event, which involved a large vertical wind oscillation exceeding 10 m/s. A nonlinear gravity wave model was able to reproduce most of the observed features. The results suggest that the wave experienced partial reflections at two altitudes and a critical layer in between, resulting in large vertical wind amplitude and multi-layer distribution of wave energy.

  2. [Medical education at Universidad de los Andes, Santiago, Chile].

    PubMed

    Orrego Vicuña, F

    1997-07-01

    Universidad de los Andes School of Medicine started in 1991 with a new medical curriculum aimed at providing a medical education for its students, that is, it attempts to give, together with technical proficiency in medical matters, formation of character and a strong ethical attitude. The curriculum lasts for seven years: five of basic, pre-clinical and clinical theoretical and practical courses, followed by two years of internships in Internal Medicine, Surgery, Obstetrics and Pediatrics, plus a four month period of an elective internship. The courses have an integrated design, in which each matter is presented from multiple perspectives, e.g. in Internal Medicine together with the clinical aspects of disease, the pathophysiology and the pharmacology of the drugs used are presented. Also the Pathology of each disease is given in coordination in the Pathology course. General educational matters such as Anthropology, Psychology, Origin of Living Beings, Theology and Medical Ethics are interspersed in the curriculum. An important feature is the personal counselling system, in which each student may choose an academic counsellor and discuss with him (her) the subjects of his choosing. Clinical practice is given in a system that includes five hospitals and five private clinics that range from general medical practice to Psychiatry or Ophthalmology.

  3. Membrane triangles with corner drilling freedoms. II - The ANDES element

    NASA Technical Reports Server (NTRS)

    Felippa, Carlos A.; Militello, Carmelo

    1992-01-01

    This is the second article in a three-part series on the construction of 3-node, 9-dof membrane elements with normal-to-its-plane rotational freedoms (the so-called drilling freedoms) using parametrized variational principles. In this part, one such element is derived within the context of the assumed natural deviatoric strain (ANDES) formulation. The higher-order strains are obtained by constructing three parallel-to-sides pure-bending modes from which natural strains are obtained at the corner points and interpolated over the element. To attain rank sufficiency, an additional higher-order 'torsional' mode, corresponding to equal hierarchical rotations at each corner with all other motions precluded, is incorporated. The resulting formulation has five free parameters. When these parameters are optimized against pure bending by energy balance methods, the resulting element is found to coalesce with the optimal EFF element derived in Part I. Numerical integration as a strain filtering device is found to play a key role in this achievement.

  4. Active Folding of the Tame Anticline, Eastern Foothills, Colombian Andes

    NASA Astrophysics Data System (ADS)

    Veloza-Fajardo, G.; Taylor, M. H.; Mora, A.; Stockli, D. F.

    2011-12-01

    We integrate neotectonic mapping and interpretation of seismic reflection profiles to evaluate the kinematics of folding and development of the Quaternary Tame anticline and Cusiana fault at 6.5 N Latitude in the eastern foothills of the Eastern Cordillera of Colombia. The Tame anticline is located approximately 660 km to the east of the Nazca-South America and 810 km to the south of the Caribbean-South America subduction zones plate boundaries in a retroarc foreland basin setting. The Tame anticline is an elongated, N15E trending structure, 14 km long N-S by 6 km wide E-W, that represents the most frontal active structure of the northern Colombian Andes. The Tame fold is related to the east-directed Cusiana fault that day lights to the south. Seismic reflection profiles indicate the Cusiana fault is a listric, west-dipping blind structure. The east flowing antecedent Macaguana creek has incised the Tame fold forming three prominent terrace levels, uplifted approximately 220, 150 and 100 meters, above current river levels. The surfaces were sampled for terrestrial cosmogenic nuclides using the depth profiling approach to account for inheritance. Surface exposure ages from the highest to lowest surfaces are 93.9, 50.8 and 32.4 kyrs at the 1σ level respectively, which were calculated using Monte Carlo methods. Trishear kinematic modeling was used to retrodeform the folding history and based on the surface abandonment ages, we will present shortening rates at millennial timescales.

  5. Over three millennia of mercury pollution in the Peruvian Andes.

    PubMed

    Cooke, Colin A; Balcom, Prentiss H; Biester, Harald; Wolfe, Alexander P

    2009-06-01

    We present unambiguous records of preindustrial atmospheric mercury (Hg) pollution, derived from lake-sediment cores collected near Huancavelica, Peru, the largest Hg deposit in the New World. Intensive Hg mining first began ca. 1400 BC, predating the emergence of complex Andean societies, and signifying that the region served as a locus for early Hg extraction. The earliest mining targeted cinnabar (HgS) for the production of vermillion. Pre-Colonial Hg burdens peak ca. 500 BC and ca. 1450 AD, corresponding to the heights of the Chavín and Inca states, respectively. During the Inca, Colonial, and industrial intervals, Hg pollution became regional, as evidenced by a third lake record approximately 225 km distant from Huancavelica. Measurements of sediment-Hg speciation reveal that cinnabar dust was initially the dominant Hg species deposited, and significant increases in deposition were limited to the local environment. After conquest by the Inca (ca. 1450 AD), smelting was adopted at the mine and Hg pollution became more widely circulated, with the deposition of matrix-bound phases of Hg predominating over cinnabar dust. Our results demonstrate the existence of a major Hg mining industry at Huancavelica spanning the past 3,500 years, and place recent Hg enrichment in the Andes in a broader historical context. PMID:19451629

  6. Dendrogeomorphic reconstruction of flash floods in the Patagonian Andes

    NASA Astrophysics Data System (ADS)

    Casteller, Alejandro; Stoffel, Markus; Crespo, Sebastián; Villalba, Ricardo; Corona, Christophe; Bianchi, Emilio

    2015-01-01

    Flash floods represent a significant natural hazard in small mountainous catchments of the Patagonian Andes and have repeatedly caused loss to life and infrastructure. At the same time, however, documentary records of past events remain fairly scarce and highly fragmentary in most cases. In this study, we therefore reconstruct the spatiotemporal patterns of past flash flood activity along the Los Cipreses torrent (Neuquén, Argentina) using dendrogeomorphic methods. Based on samples from Austrocedrus chilensis, Pseudotsuga menziesii, and Nothofagus dombeyi, we document 21 flash flood events covering the period A.D. 1890-2009 and reconstruct mean recurrence intervals of events at the level of individual trees being impacted, which varies from 4 to 93 years. Results show that trees tend to be older (younger) in sectors of the torrent with gentler (steeper) slope gradients. Potential triggers of flash floods were analyzed using daily temperature and precipitation data from a nearby weather station. Weather conditions leading to flash floods are abundant precipitations during one to three consecutive days, combined with temperatures above the rain/snow threshold (2 °C) in the whole watershed.

  7. Quaternary Glaciations in the Rio Mendoza Valley, Argentine Andes

    NASA Astrophysics Data System (ADS)

    Espizua, Lydia E.

    1993-09-01

    In the Rio Mendoza valley, five Pleistocene drifts and one Holocene drift are distinguished by multiple relative-age criteria, including surface-rock weathering, development of rock varnish, moraine morphology, soil-profile development, and stratigraphic relationships. Several absolute ages suggest a preliminary chronology. During the oldest (Uspallata) glaciation, a system of valley glaciers flowed 110 km from the Andean drainage divide and 80 km from Cerro Aconcagua to terminate at 1850 m. Drift of this ice advance is older than a widespread tephra dated by fission-track at 360,000 ± 36,000 yr. During the Punta de Vacas advance, ice terminated at 2350 m, while during the subsequent Penitentes advance, the glacier system ended at 2500 m. A travertine layer overlying Penitentes Drift has U-series age of 24,200 ± 2000 yr B.P. The distribution of Horcones Drift, which is inferred to represent the last glacial maximum, delimits an independent ice stream that flowed 22 km down Horcones valley to 2750 m. A later readvance (Almacenes) reached 3250 m. Confluencia Drift is considered to be Neoglacial in age and extends downvalley to 3300 m. The moraine sequence is compared with those studied by Caviedes (1972) along Rio Aconcagua on the Chilean flank of the Andes.

  8. POTENTIAL IMPACTS OF CLIMATE CHANGE ON THE TROPICAL ANDES

    NASA Astrophysics Data System (ADS)

    Soria, Freddy; Kazama, So

    In this paper are investigated the net radiation (Rn) and the potential glacier melt discharge trends in a glacier in the tropical Andes, for the assessment of climate change impacts on the water resources availability in remote regions. It is assessed the applicability of remote sensing techniques, through the performance evaluation of the Surface and Energy Balance algorithm (SEBAL). For the calibration it is used ground data observed on the ablation surface of the Zongo glacier in Bolivia. The potential climate change impacts quantified are on the glacier melt discharge. The inferences are calibrated in the period 2004-2007. Results show that the SEBAL performance is adequate from an engineering perspective (Root Mean Square Error for albedo estimations are 0.15, in average). Climate change impacts for the period 1986-2005 are an increase of 42% in the Rn, and the loss in the glacier ablation area of 37% (both in reference to 1986). The melt from the studied glacier in the period 2004-2007 is estimated to produce a maximum potential energy of 3.1 [MW h] in average per day (dry season), which in the practice can be used to quantify the potential impacts of the climate change in partially glacierized catchments.

  9. Over three millennia of mercury pollution in the Peruvian Andes

    PubMed Central

    Cooke, Colin A.; Balcom, Prentiss H.; Biester, Harald; Wolfe, Alexander P.

    2009-01-01

    We present unambiguous records of preindustrial atmospheric mercury (Hg) pollution, derived from lake-sediment cores collected near Huancavelica, Peru, the largest Hg deposit in the New World. Intensive Hg mining first began ca. 1400 BC, predating the emergence of complex Andean societies, and signifying that the region served as a locus for early Hg extraction. The earliest mining targeted cinnabar (HgS) for the production of vermillion. Pre-Colonial Hg burdens peak ca. 500 BC and ca. 1450 AD, corresponding to the heights of the Chavín and Inca states, respectively. During the Inca, Colonial, and industrial intervals, Hg pollution became regional, as evidenced by a third lake record ≈225 km distant from Huancavelica. Measurements of sediment-Hg speciation reveal that cinnabar dust was initially the dominant Hg species deposited, and significant increases in deposition were limited to the local environment. After conquest by the Inca (ca. 1450 AD), smelting was adopted at the mine and Hg pollution became more widely circulated, with the deposition of matrix-bound phases of Hg predominating over cinnabar dust. Our results demonstrate the existence of a major Hg mining industry at Huancavelica spanning the past 3,500 years, and place recent Hg enrichment in the Andes in a broader historical context. PMID:19451629

  10. Crustal contributions to arc magmatism in the Andes of Central Chile

    USGS Publications Warehouse

    Hildreth, W.; Moorbath, S.

    1988-01-01

    Fifteen andesite-dacite stratovolcanoes on the volcanic front of a single segment of the Andean arc show along-arc changes in isotopic and elemental ratios that demonstrate large crustal contributions to magma genesis. All 15 centers lie 90 km above the Benioff zone and 280??20 km from the trench axis. Rate and geometry of subduction and composition and age of subducted sediments and seafloor are nearly constant along the segment. Nonetheless, from S to N along the volcanic front (at 57.5% SiO2) K2O rises from 1.1 to 2.4 wt %, Ba from 300 to 600 ppm, and Ce from 25 to 50 ppm, whereas FeO*/MgO declines from >2.5 to 1.4. Ce/Yb and Hf/Lu triple northward, in part reflecting suppression of HREE enrichment by deep-crustal garnet. Rb, Cs, Th, and U contents all rise markedly from S to N, but Rb/Cs values double northward - opposite to prediction were the regional alkali enrichment controlled by sediment subduction. K/Rb drops steeply and scatters greatly within many (biotite-free) andesitic suites. Wide diversity in Zr/Hf, Zr/Rb, Ba/Ta, and Ba/La within and among neighboring suites (which lack zircon and alkali feldspar) largely reflects local variability of intracrustal (not slab or mantle) contributions. Pb-isotope data define a limited range that straddles the Stacey-Kramers line, is bracketed by values of local basement rocks, in part plots above the field of Nazca plate sediment, and shows no indication of a steep (mantle+sedimentary) Pb mixing trend. 87Sr/86Sr values rise northward from 0.7036 to 0.7057, and 143Nd/144Nd values drop from 0.5129 to 0.5125. A northward climb in basal elevation of volcanic-front edifices from 1350 m to 4500 m elevation coincides with a Bougueranomaly gradient from -95 to -295 mgal, interpreted to indicate thickening of the crust from 30-35 km to 50-60 km. Complementary to the thickening crust, the mantle wedge beneath the front thins northward from about 60 km to 30-40 km (as slab depth is constant). The thick northern crust contains an abundance of Paleozoic and Triassic rocks, whereas the proportion of younger arc-intrusive basement increases southward. Primitive basalts are unknown anywhere along the arc. Base-level isotopic and chemical values for each volcano are established by blending of subcrustal and deep-crustal magmas in zones of melting, assimilation, storage and homogenization (MASH) at the mantle-crust transition. Scavenging of mid-to upper-crustal silicic-alkalic melts and intracrustal AFC (prominent at the largest center) can subsequently modify ascending magmas, but the base-level geochemical signature at each center reflects the depth of its MASH zone and the age, composition, and proportional contribution of the lowermost crust. ?? 1988 Springer-Verlag.

  11. A Bayesian Approach for Apparent Inter-plate Coupling in the Central Andes Subduction Zone

    NASA Astrophysics Data System (ADS)

    Ortega Culaciati, F. H.; Simons, M.; Genrich, J. F.; Galetzka, J.; Comte, D.; Glass, B.; Leiva, C.; Gonzalez, G.; Norabuena, E. O.

    2010-12-01

    We aim to characterize the extent of apparent plate coupling on the subduction zone megathrust with the eventual goal of understanding spatial variations of fault zone rheology, inferring relationships between apparent coupling and the rupture zone of big earthquakes, as well as the implications for earthquake and tsunami hazard. Unlike previous studies, we approach the problem from a Bayesian perspective, allowing us to completely characterize the model parameter space by searching a posteriori estimates of the range of allowable models instead of seeking a single optimum model. Two important features of the Bayesian approach are the possibility to easily implement any kind of physically plausible a priori information and to perform the inversion without regularization, other than that imposed by the way in which we parameterize the forward model. Adopting a simple kinematic back-slip model and a 3D geometry of the inter-plate contact zone, we can estimate the probability of apparent coupling (Pc) along the plate interface that is consistent with a priori information (e.g., approximate rake of back-slip) and available geodetic measurements. More generally, the Bayesian approach adopted here is applicable to any region and eventually would allow one to evaluate the spatial relationship between various inferred distributions of fault behavior (e.g., seismic rupture, postseismic creep, and apparent interseismic coupling) in a quantifiable manner. We apply this methodology to evaluate the state of apparent inter-seismic coupling in the Chilean-Peruvian subduction margin (12 S - 25 S). As observational constraints, we use previously published horizontal velocities from campaign GPS [Kendrick et al., 2001, 2006] as well as 3 component velocities from a recently established continuous GPS network in the region (CAnTO). We compare results from both joint and independent use of these data sets. We obtain patch like features for Pc with higher values located above 60 km depth. We identify a strong correlation between the features of high Pc and the regions associated with the rupture process of the 1995 (Mw 8.1) Antofagasta, 2001 (Mw 8.4) Arequipa and the 2007 (Mw 8.0) Pisco, earthquakes; as well as the region identified as the Arica bend seismic gap, which has not experienced a large earthquake since 1877.

  12. Cooling History for the Sierra Laguna Blanca (NW Argentina) on the Southern Puna Plateau, Central Andes

    NASA Astrophysics Data System (ADS)

    Zhou, R.; Schoenbohm, L. M.; Sobel, E. R.; Stockli, D. F.; Glodny, J.

    2014-12-01

    Various dynamic models have been proposed to explain deformation history and topographic evolution for the southern Altiplano-Puna Plateau, including inversion of the Cretaceous Salta rift structures, formation of an orogenic wedge, flat subduction, climate-tectonic coupling, and lithospheric foundering. Controversies persist in the southern Puna Plateau, where preexisting rift structures are unknown and Cenozoic shortening events are sparsely documented. The 6-km high Sierra Laguna Blanca (LB) (NW Argentina) is among the most outstanding topographic features in the interior of the southern Puna Plateau. We document cooling history for LB with apatite (U-Th)/He, apatite fission-track and zircon (U-Th)/He thermochronometers for a vertical profile from 3.6-5.6 km on its eastern flank. Preliminary results from apatite fission-track (AFT) analysis yield ages ranging from 45-65 Ma, with top samples being the oldest. Dpar values for all samples are low (1.54 to 1.74), suggesting a relatively low-temperature partial annealing zone. All samples have shortened mean track lengths ranging from 10.9 to 12.3 micrometers, suggesting partial resetting. Preliminary apatite U-Th/He (AHe) ages are compatible with AFT ages but are widely dispersed, perhaps due to U zoning and small U-rich inclusions which have been observed on AFT external detectors. Inverse modeling of AFT data and selected AHe data using the HeFTy program reveal two major cooling events for LB. All models start ~90-70 Ma and immediately decrease their temperatures to ~60°C before ~50 Ma. Samples may have stayed ~60°C without additional thermal events until ~15-10 Ma, when the most recent cooling event took place, bringing all samples to surface temperature. Our first finding is that the interior of the southern Puna Plateau may have been influenced by the Salta Rift during the Cretaceous, extending the known zone of influence further west. Second, the most recent cooling phase (mid-late Miocene) is consistent with out-of-sequence deformation in the southern Puna Plateau, which might be genetically linked to a proposed lithospheric dripping event.

  13. A novel species of Euspondylus (Squamata: Gymnophthalmidae) from the Andes Mountains of central Peru.

    PubMed

    Doan, Tiffany M; Adams, Grant

    2015-10-21

    The South American gymnophthalmid genus Euspondylus is distributed from Venezuela through Peru, with its highest diversity occurring in Peru. Euspondylus paxcorpus sp. nov. is a new species from Junín, Peru possessing prefrontal scales and represented by 60 specimens. The new species differs from all other species by the combination of four supraoculars with supraocular/supraciliary fusion, 5-7 occipitals, a single palpebral scale, five supralabials and infralabials, quadrangular dorsal scales with low keels arranged in transverse series only, 40-45 in a longitudinal count and 22-28 in a transverse count, 12 rows of ventrals in a transverse count and 23-25 in a longitudinal count, and no sexual dimorphism in coloration. The discovery of E. paxcorpus increases the known number of Euspondylus species to 13. Because the coloration patterns of the specimens were greatly different after preservation in alcohol, caution should be used when identifying Euspondylus species from museum specimens.

  14. Petrological characteristics of Plio-Quaternary 'Sencca' Ignimbrites, Western Cordillera of the Central Andes in Peru

    NASA Astrophysics Data System (ADS)

    Çubukçu, H. E.; Gerbe, M.-C.; Thouret, J.-C.; de la Rupelle, A.; Boivin, P.

    2012-04-01

    Large-volume ignimbrite deposits have been emplaced between 24.6 and 1.37 Ma in the western Andean Cordillera of Southern Peru. The ignimbrites older than 9 Ma (Nazca, Alpabamba, Huaylillas and Caraveli ignimbrites) have formed plateaus, whereas the deep valleys incised in plateaus have been filled by younger Lower-Upper Sencca (~5- 2 Ma) and Las Lomas ignimbrites. Among the younger valley-filling units, Lower and Upper Sencca ignimbrites, with intercalated Upper Barroso lavas, have probably originated from a source beneath the Nevado Coropuna volcano. The unwelded-to-loose, crystal-poor pumice flows of Las Lomas unit (c.1.56-1.37 Ma) can be readily distinguished in the field from the rhyolitic Sencca ignimbrites. In contrast, discriminating Lower Sencca from Upper Sencca deposits in the field is difficult due to comparable lithofacies characteristics. Such a distinction is, however, essential in order to determine temporal constraints on valley incision. The Lower Sencca compound ignimbrite sheet is more widespread (~800 km2) than the Upper Sencca ignimbrite sheet (~600 km2). The Lower Sencca ignimbrites usually form terraces hanging on valley sides but Upper Sencca form deposits crop out near the present valley bottoms or in shallow valleys on high plateaus around Barroso volcanoes. The Lower Sencca ignimbrite is composed of multiple cooling units with a crystal- and fiamme-rich vitrophyric base, overlain by strongly welded, eutaxitic subunits towards the top. Uppermost subunits exhibit an indurated ash and pumice rich vapour-phase facies. The Upper Sencca ignimbrite sheet comprises two subunits only: (1) the basal, black vitrophyre, overlain by a fiamme- and crystal-rich, strongly welded, eutaxitic subunit; 2) the upper subunit with an indurated or slightly welded, crystal-poor, pumice-rich vapour phase facies The dominant mineralogy of Lower Sencca compound ignimbrites includes plagioclase (An13-68) + alkali feldspar (Or38-65) + biotite (XMg: Mg/Mg+Fe= 0.62-0.69) + clinopyroxene (Wo38-46En35-46Fs14-20) + orthopyroxene (Mg#: 0.68-0.78) + ilmenite (Ilm: 73-77%) + (titano)-magnetite (Usp: 16-36%) with accessory quartz, apatite and zircon. The mineralogical assemblage of Upper Sencca ignimbrite sheet consists of plagioclase (An6-44) + biotite (XMg: 0.66-0.69) + clinopyroxene (Wo40-43En42-43Fs13-19) + orthopyroxene (Mg#: 0.69-0.73) + ilmenite (Ilm: 40-76%) + (titano)magnetite (Usp: 8-28%) with accessory quartz, apatite and zircon. Although Lower and Upper Sencca ignimbrites bear similar mineralogical assemblages, they exhibit different geochemical characteristics. Lower Sencca is relatively enriched in incompatible elements: Concentrations of Th (15-33 ppm), Nb (10-24 ppm), Ta (1-2 ppm), Y (12-30 ppm), Sm (4-11 ppm) and Rb (121-241 ppm) are higher than those of Upper Sencca, with Th (6-22 ppm), Nb (9-17 ppm), Ta (0.5-1.5 ppm), Y (4-24 ppm), Sm (1-8 ppm) and Rb (92-195 ppm). However, the ratios of incompatible elements between the two episodes of Sencca ignimbrite-forming eruptions are nearly constant (Ce/Yb ~45-55, La/Yb ~20-30). This indicates that both Sencca magmas have probably been originated from similar parental magmas. The more evolved composition of Lower Sencca contrasting with the less evolved nature of the Upper Sencca magma and Upper Barroso lavas indicate a probable replenishment of magmatic reservoir(s) following the emplacement of Lower Sencca ignimbrites. Initial Sr-isotope ratios and epsilon-Nd of the Upper Sencca ignimbrite are quite homogeneous ranging from 0.70593 to 0.70651 and from -3.76 to 3.06, respectively, whereas those of the Lower Sencca are more variable from 0.70502 to 0.70655 and +3.04 to -2.04. Nevertheless, Sencca magmatic isotopic signatures are less variable than that of the older ignimbrites.

  15. The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Phytophthora infestans is a destructive plant pathogen best known for causing the disease that triggered the Irish potato famine and continues to be the most costly potato pathogen to manage worldwide. Identification of its elusive center of origin is critical to understanding the mechanisms of repe...

  16. [Biomass recovery through secondary succession in the Cordillera Central de los Andes, Colombia].

    PubMed

    del Valle, Jorge Ignacio; Restrepo, Héctor Iván; Londoño, Mónica María

    2011-09-01

    Estimations on biomass recovery rates by secondary tropical forests are needed to understand the complex tropical succession, and their importance on CO2 capture, to offset the warming of the planet. We conducted the study in the Porce River Canyon between 550 and 1 700m.a.s.l. covering tropical and premontane moist belts. We established 33 temporary plots of 50m x 20m in secondary forests, including fallows to succesional forests, and ranging between 3 and 36 years old; we measured the diameter at breast height (D) of all woody plants with D > or = 5cm. In each one of these plots we established five 10m x 10m subplots, in which we measured the diameter betweem 1cm < or = D < 5cm of all woody plants. We estimated the biomass of pastures by harvesting 54 plots of 2m x 2m, and of shrubs in the fallows by harvesting the biomass in 18 plots of 5m x 2m. We modeled Bav (above ground live biomass of woody plants) and Brg (coarse root biomass) as a function of succesional age (t) with the growth model of von Bertalanffy, using 247t/ha and 66t/ha as asymptote, respectively. Besides, we modeled the ratios brg/bav = f(D) and Brg/Bav = f(t). The model estimated that 87 years are required to recover the existing Bav of primary forests through secondary succession, and 217 years for the Brg of the primary forest. The maximum instantaneous growth rate of the Bav was 6.95 t/ha/yr at age 10. The maximum average growth rate of the Bav was 6.26 t/ha/yr at age 17. The weighted average of the absolute growth rate of the Bav reached 4.57t/ha/yr and the relative growth rate 10% annually. The ratio brg/bav decreases with increasing D. The ratio Brg/Bav initially increases very rapidly until age 5 (25%), then decreases to reach 25 years (18%) and increases afterwards until the ratio reaches the asymptote (26.7%). PMID:22017137

  17. The age and constitution of Cerro Campanario, a mafic stratovolcano in the Andes of central Chile

    USGS Publications Warehouse

    Hildreth, W.; Singer, B.; Godoy, E.; Munizaga, F.

    1998-01-01

    Cerro Campanario, a towering landmark on the continental divide near Paso Pehuenche, is a glacially eroded remnant of a mafic stratovolcano that is much younger than previously supposed. Consisting of fairly uniform basaltic andesite, rich in olivine and plagioclase, the 10-15 km3 edifice grew rapidly near the end of the middle Pleistocene, about 150-160 ka, as indicated by 40Ar/39Ar and unspiked K-Ar analyses of its lavas.

  18. Volcano deformation survey over the Northern and Central Andes with ALOS InSAR time series

    NASA Astrophysics Data System (ADS)

    Morales Rivera, Anieri M.; Amelung, Falk; Mothes, Patricia

    2016-07-01

    We use ALOS-1 Interferometric Synthetic Aperture Radar data spanning the period of 2007-2011 to obtain time-dependent ground deformation data over all of the volcanoes in Colombia, Ecuador, and Peru. We detect deformation on or near the proximity of Galeras, Reventador, Tungurahua, Guagua Pichincha, Sangay, and Cerro Auquihuato volcanoes, uncovering previously undocumented deformation in the latter three. Deformation is attributed to changes in pressurization of the volcanic systems (Galeras, Tungurahua, Guagua Pichincha, and Cerro Auquihuato), subsidence associated with flow deposits (Reventador), and flank creep (Sangay). Our models suggest that the pressure sources are located at depths of ˜1-6 km from the surface, indicating that the measurable deformation within our data is restricted to shallow magma chambers and hydrothermal systems.

  19. The Puelche volcanic field: Extensive Pleistocene rhyolite lava flows in the Andes of central Chile

    USGS Publications Warehouse

    Hildreth, W.; Fierstein, J.; Godoy, E.; Drake, Robert E.; Singer, B.

    1999-01-01

    A remote volcanic field in the rugged headwaters of the Rio Puelche and Rio Invernada (35.8??S) constitutes the largest cluster of Quaternary rhyolite lava flows yet identified in the Andean Southern Volcanic Zone. The Puelche Volcanic Field belongs to an intra-arc belt of silicic magmatic centers that extends, at least, 140 km north-south and lies well east of the volcanic front but nonetheless considerably west of the intraplate extensional fields of basaltic and alkaline centers of pampean Argentina. The authors' mapping has distinguished one shallow intrusive mass of early Pleistocene biotite rhyodacite (70.5% SiO2), 11 eruptive units of mid-Pleistocene high-K biotite-rhyolite lava (71.3-75.6% SiO2), and 4 eruptive units of basaltic andesite (53.95-4.9% SiO2), the conduits of which cut some of the rhyolites. Basal contacts of the rhyolite lava flows (and subjacent pyroclastic precursors) are generally scree covered, but glacial erosion has exposed internal flow structures and lithologic zonation superbly. Thicknesses of individual rhyolite lava flows range from 75 m to 400 m. Feeders for several units are well exposed. Cliff-draping unconformities and intracanyon relationships among the 11 rhyolite units show that the eruptive sequence spanned at least one glacial episode that accentuated the local relief. Lack of ice-contact features suggests, however, that all or most eruptions took place during non-glacial intervals probably between 400 ka and 100 ka. Post-eruptive glacial erosion reduced the rhyolites to several non-contiguous remnants that altogether cover 83 km2 and represent a surviving volume of about 21 km3. Consideration of slopes, lava thicknesses, and paleotopography suggest that the original area and volume were each about three times greater. Phenocryst content of the rhyolites ranges from 1 to 12%, with plagioclase>>biotite>FeTi oxides in all units and amphibole conspicuous in the least silicic. The chemically varied basaltic andesites range from phenocryst-poor to phenocryst-rich, exhibiting large differences in proportions of clinopyroxene, olivine, plagioclase, and xenocrystic quartz. Compositional bimodality of the volcanic field is striking, there being no Quaternary eruptive units having SiO2 contents between 55 and 70%. Major and trace element compositions of the mafic and silicic rocks are nonetheless typical of continental-margin arc suites, not of intracontinental suites. The lack of intermediate eruptive units and the differences between the mafic and rhyolitic lavas in Sr-isotope composition suggest that the rhyolites fractionated from a hybrid parent rather than continuously from basaltic magma. The rhyolites may contain larger contributions of upper-crustal partial melts than do silicic products of the volcanic-front centers 30 km to the west.

  20. Sketch on the structural geology and vulcanism in the Central High Plateau of the Bolivian Andes

    NASA Technical Reports Server (NTRS)

    Brockmann, C. E. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. The Earth Resources Technology Satellite Program has as an objective the development of tectonic maps for Bolivia. Maps were prepared using the images of ERTS-1 in a preliminary study of alignments observed and rapidly interpreted in images 1010-14033-3-4-5-6-7 on a scale of 1:1,000,000, and later verified on the ground with corresponding fault zones. This information was not shown on existing geologial maps. The ERTS-1 imagery was used in volcanology research for drawing the regional limits of volcanic formations as soon as the alignment and the extent of the volcanoes could be determined. The extensive coverage of ERTS-1 images provides an excellent opportunity for developing studies of regional structures.

  1. The Andes Virus Nucleocapsid Protein Directs Basal Endothelial Cell Permeability by Activating RhoA

    PubMed Central

    Gorbunova, Elena E.; Simons, Matthew J.; Gavrilovskaya, Irina N.

    2016-01-01

    ABSTRACT Andes virus (ANDV) predominantly infects microvascular endothelial cells (MECs) and nonlytically causes an acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). In HPS patients, virtually every pulmonary MEC is infected, MECs are enlarged, and infection results in vascular leakage and highly lethal pulmonary edema. We observed that MECs infected with the ANDV hantavirus or expressing the ANDV nucleocapsid (N) protein showed increased size and permeability by activating the Rheb and RhoA GTPases. Expression of ANDV N in MECs increased cell size by preventing tuberous sclerosis complex (TSC) repression of Rheb-mTOR-pS6K. N selectively bound the TSC2 N terminus (1 to 1403) within a complex containing TSC2/TSC1/TBC1D7, and endogenous TSC2 reciprocally coprecipitated N protein from ANDV-infected MECs. TSCs normally restrict RhoA-induced MEC permeability, and we found that ANDV infection or N protein expression constitutively activated RhoA. This suggests that the ANDV N protein alone is sufficient to activate signaling pathways that control MEC size and permeability. Further, RhoA small interfering RNA, dominant-negative RhoA(N19), and the RhoA/Rho kinase inhibitors fasudil and Y27632 dramatically reduced the permeability of ANDV-infected MECs by 80 to 90%. Fasudil also reduced the bradykinin-directed permeability of ANDV and Hantaan virus-infected MECs to control levels. These findings demonstrate that ANDV activation of RhoA causes MEC permeability and reveal a potential edemagenic mechanism for ANDV to constitutively inhibit the basal barrier integrity of infected MECs. The central importance of RhoA activation in MEC permeability further suggests therapeutically targeting RhoA, TSCs, and Rac1 as potential means of resolving capillary leakage during hantavirus infections. PMID:27795403

  2. Petrographic and Geochemical Characterization of the Cambumbia STOCK in Andean Central Cordillera, Colombia

    NASA Astrophysics Data System (ADS)

    Rojas Lequerica, S.; Jaramillo Mejía, J.; Concha Perdomo, A.

    2012-12-01

    The Cambumbia Stock is located on the western flank of the Central Cordillera of the northern Andes. The goals of this study were to petrographic and geochemically characterize the Cambumbia igneous body and to establish its petrogenetic history. 41 samples were collected, 28 for petrographic analysis and 14 for elementary chemical determination by ICP-MS. Petrographically the samples were classified as hornblende and pyroxene-gabbros varying to diorites, gabbronorites and tonalites, the rock texture varies from medium to coarse granular grain, with local microporfiritic texture. It was concluded from the major elements analysis that the samples correspond to the sub-alkaline series with low K content, mainly in the calc-alkaline series, within the gabbros and diorites fields. By using the SiO2 vs TiO2 (Jaramillo, 1980), Th/Yb vs Ta/Yb (Pearce, 1984) (Fig. 1) and Zr/117-Th-Nb/16 (Wood, 1979) diagrams it was determined that these rocks were generated in two geotectonic environments: one type MOR (extension) and other island arc (subduction, compression). Petrographic and geochemical comparisons between the rocks of Cambumbia Stock and Diorite and Gabbro El Pueblito (Giraldo, 2009) (located about 25 km to the north-west) may postulate a possible genetic link between them. Recently, a U/Pb age was obtained by the Universidad de Caldas in zircon in 2009 (not published data), yielded an age of 233.41 ± 3.4 Ma (Middle Triassic). This age is consistent with the global event of the extension and fragmentation of Pangea supercontinent. In addition, the mantle nature of the source and the petrogenetic evolution of the magmatic system were established. References GIRALDO, M.I., (2009): Esquema geodinámica de la parte noroccidental de la cordillera Central de Colombia. (Thesis). p.56-68. Universidad Nacional de Colombia, Medellín. JARAMILLO, J.M. (1980): Petrology and geochemistry of the Nevado del Ruiz Volcano northern Andes, Colombia (Thesis). 167 p. University of Houston

  3. The First Ten Months of Investigation of Gravity Waves and Temperature Variability Over the Andes

    NASA Astrophysics Data System (ADS)

    Pugmire, Jonathan; Criddle, Neal; Taylor, Michael; Pautet, Dominique; Zhao, Yucheng

    2010-10-01

    The Andes region is an excellent natural laboratory for investigating gravity wave influences on the Upper Mesospheric and Lower Thermospheric (MLT) dynamics. The instrument suite that comprised the very successful Maui-MALT program was recently re-located to a new Andes Lidar Observatory (ALO) located at Cerro Pachon, Chile to obtain in-depth seasonal measurements of MLT dynamics over the Andes mountains. As part of the instrument set the Utah State University CEDAR Mesospheric Temperature Mapper (MTM) has operated continuously since August 2009 measuring the near infrared OH(6,2) band and the O2(0,1) Atmospheric band intensity and temperature perturbations. This poster focuses on an analysis of nightly OH temperatures and the observed variability, as well as selected gravity wave events illustrating the high wave activity and its diversity.

  4. Traditional use of the Andean flicker (Colaptes rupicola) as a galactagogue in the Peruvian Andes

    PubMed Central

    Froemming, Steve

    2006-01-01

    This paper explores the use of the dried meat and feathers of the Andean Flicker (Colaptes rupicola) to increase the milk supply of nursing women and domestic animals in the Andes. The treatment is of preColumbian origin, but continues to be used in some areas, including the village in the southern Peruvian highlands where I do ethnographic research. I explore the factors giving rise to and sustaining the practice, relate it to other galactagogues used in the Andes and to the use of birds in ethnomedical and ethnoveterinary treatments in general, and situate it within the general tendency in the Andes and elsewhere to replicate human relations in the treatment of valuable livestock. The bird's use as a galactagogue appears to be motivated by both metaphorical associations and its perceived efficacy, and conceptually blends human and animal healthcare domains. PMID:16677398

  5. STS-65 Earth observation of Northern Chile and Andes Mtns taken from OV-102

    NASA Technical Reports Server (NTRS)

    1994-01-01

    STS-65 Earth observation taken aboard Columbia, Orbiter Vehicle (OV) 102, shows Northern Chile and the Andes Mountains. This color photograph is a panoramic (southern view) that features Chile and the Andes Mountains of South America. The Atacama Desert, one of the driest regions on Earth, is clearly visible along the Chilean coast. In the near left foreground is the Salar de Arizaro. Salar Punta Negra in the center foreground appears to be partially filled with water. On the right side of the view, a coastal plateau rises from the Pacific Ocean and meets the Andes Mountains that appear as a backbone running north to south along the border of Chile and Argentina. In the distant left portion of the view can be seen the hazy Chaco Plains and Pampas.

  6. Contrasting climate change impact on river flows from high-altitude catchments in the Himalayan and Andes Mountains

    PubMed Central

    Pellicciotti, Francesca

    2016-01-01

    Mountain ranges are the world’s natural water towers and provide water resources for millions of people. However, their hydrological balance and possible future changes in river flow remain poorly understood because of high meteorological variability, physical inaccessibility, and the complex interplay between climate, cryosphere, and hydrological processes. Here, we use a state-of-the art glacio-hydrological model informed by data from high-altitude observations and the latest climate change scenarios to quantify the climate change impact on water resources of two contrasting catchments vulnerable to changes in the cryosphere. The two study catchments are located in the Central Andes of Chile and in the Nepalese Himalaya in close vicinity of densely populated areas. Although both sites reveal a strong decrease in glacier area, they show a remarkably different hydrological response to projected climate change. In the Juncal catchment in Chile, runoff is likely to sharply decrease in the future and the runoff seasonality is sensitive to projected climatic changes. In the Langtang catchment in Nepal, future water availability is on the rise for decades to come with limited shifts between seasons. Owing to the high spatiotemporal resolution of the simulations and process complexity included in the modeling, the response times and the mechanisms underlying the variations in glacier area and river flow can be well constrained. The projections indicate that climate change adaptation in Central Chile should focus on dealing with a reduction in water availability, whereas in Nepal preparedness for flood extremes should be the policy priority. PMID:27482082

  7. Contrasting climate change impact on river flows from high-altitude catchments in the Himalayan and Andes Mountains.

    PubMed

    Ragettli, Silvan; Immerzeel, Walter W; Pellicciotti, Francesca

    2016-08-16

    Mountain ranges are the world's natural water towers and provide water resources for millions of people. However, their hydrological balance and possible future changes in river flow remain poorly understood because of high meteorological variability, physical inaccessibility, and the complex interplay between climate, cryosphere, and hydrological processes. Here, we use a state-of-the art glacio-hydrological model informed by data from high-altitude observations and the latest climate change scenarios to quantify the climate change impact on water resources of two contrasting catchments vulnerable to changes in the cryosphere. The two study catchments are located in the Central Andes of Chile and in the Nepalese Himalaya in close vicinity of densely populated areas. Although both sites reveal a strong decrease in glacier area, they show a remarkably different hydrological response to projected climate change. In the Juncal catchment in Chile, runoff is likely to sharply decrease in the future and the runoff seasonality is sensitive to projected climatic changes. In the Langtang catchment in Nepal, future water availability is on the rise for decades to come with limited shifts between seasons. Owing to the high spatiotemporal resolution of the simulations and process complexity included in the modeling, the response times and the mechanisms underlying the variations in glacier area and river flow can be well constrained. The projections indicate that climate change adaptation in Central Chile should focus on dealing with a reduction in water availability, whereas in Nepal preparedness for flood extremes should be the policy priority. PMID:27482082

  8. Possible future lakes in the Andes of Peru

    NASA Astrophysics Data System (ADS)

    Colonia, Daniel; Haeberli, Wilfried; Torres, Judith; Giraldez, Claudia; Schauwecker, Simone; Santiago, Alexzander; Cochachin, Alejo; Huggel, Christian

    2015-04-01

    Climate change has caused large losses of glacier mass in the Andes of Peru. Also, given the projected changes in climate, based on different IPCC scenarios for 2050 and 2080, simulations with a tropical glacier-climate model indicate that glaciers will continue to retreat. According to the national Peruvian glacier inventories 43% of glacier area has disappeared between 1970 and 2003-2010 in the 19 snowy mountain ranges and a total of 8 355 new lakes have formed in deglaciating terrain. With glacier retreat new lakes form in parts of the glacier tongue where there is an overdeepening, and these lakes can be a source of natural hazards to downstrean populations. Therefore, the identification of possible future lakes is important to plan for preventive measures concerning possible lake outbursts as well as to understand changes in freshwater storage in the corresponding source areas. Modeling of glacier-bed overdeepenings and possible future lakes forming in such topographic depressions when becoming ice-free was done using the SRTM DEM from the year 2000 with a 90 m resolution and the 2003-2010 glacier outlines from the recently published national glacier inventory of Perú. The GIS-based analysis followed three main steps: (1) identification of flat glacier areas with less than 10° surface slope as a first-order spatial approximation to possible occurrences of glacier-bed overdeepenings; (2) application, using Google Earth, of three morphological indications of glacier-bed overdeepenings following Frey et al. (2010): steepening surface slope, onset of crevasse formation, lateral flow-narrowing; and (3) verification of the results from steps (1) and (2) by comparison with GlabTop modeling of bed topographies following Linsbauer et al. (2012) using the SRTM DEM, contour lines and constructed branch lines for all glaciers. A pilot study has already been carried out for the Cordillera Blanca. The results show that 31 major new lakes may form in the future. The total

  9. Carbon stabilization mechanisms in soils in the Andes

    NASA Astrophysics Data System (ADS)

    Jansen, Boris; Cammeraat, Erik

    2015-04-01

    The volcanic ash soils of the Andes contain very large stocks of soil organic matter (SOM) per unit area. Consequently, they constitute significant potential sources or sinks of the greenhouse gas CO2. Climate and/or land use change potentially have a strong effect on these large SOM stocks. To clarify the role of chemical and physical stabilisation mechanisms in volcanic ash soils in the montane tropics, we investigated carbon stocks and stabilization mechanisms in the top- and subsoil along an altitudinal transect in the Ecuadorian Andes. The transect encompassed a sequence of paleosols under forest and grassland (páramo), including a site where vegetation cover changed in the last century. We applied selective extraction techniques, performed X-ray diffraction analyses of the clay fraction and estimated pore size distributions at various depths in the top- and subsoil along the transect. In addition, from several soils the molecular composition of SOM was further characterized with depth in the current soil as well as the entire first and the top of the second paleosol using GC/MS analyses of extractable lipids and Pyrolysis-GC/MS analyses of bulk organic matter. Our results show that organic carbon stocks in the mineral soil under forest a páramo vegetation were roughly twice as large as global averages for volcanic ash soils, regardless of whether the first 30cm, 100cm or 200cm were considered. We found the carbon stabilization mechanisms involved to be: i) direct stabilization of SOM in organo-metallic (Al-OM) complexes; ii) indirect protection of SOM through low soil pH and toxic levels of Al; and iii) physical protection of SOM due to a very high microporosity of the soil (Tonneijck et al., 2010; Jansen et al. 2011). When examining the organic carbon at a molecular level, interestingly we found extensive degradation of lignin in the topsoil while extractable lipids were preferentially preserved in the subsoil (Nierop and Jansen, 2009). Both vegetation

  10. Two New Species of Black Flies (Diptera: Simuliidae) from the High Andes of Colombia.

    PubMed

    Mantilla, Juan S; Moncada, Ligia I; Matta, Nubia E; Adler, Peter H

    2013-01-01

    The females, males, pupae, and larvae of two new species of Simulium are described and illustrated from a small stream 3950 m above sea level in the Lake Otún area of the Colombian Andes Mountains. Simulium (Pternaspatha) quimbayium n. sp. represents a 630-km northeastern extension of the distributional range of previously known members of the subgenus Pternaspatha, and Simulium (Psilopelmia) machetorum n. sp. represents the highest altitude recorded for a species of the subgenus Psilopelmia. These species illustrate the unique simuliid biodiversity in the páramo ecosystem of the high northern Andes.

  11. Erosion by Ice and Water in the Southern Andes

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This scene on the remote, rugged Argentine/Chilean border in the far southern Andes Mountains offers numerous, dramatic examples of both erosional processes and features of ice and water. The sharp, glaciated crest of the Cerro San Lorenzo (center) exceeds 12,000 feet and casts a long shadow southeastward. Glaciers on its western flank flow into the valley. This Electronic Still Camera photo was taken from the International Space Station, in December 2000 (late spring) when most of the previous winter's snow had melted below an altitude of 6,000 feet. Lago Pueyrredon, and the other lakes visible here, have been excavated by geologically recent episodes of glacier erosion, when glaciers extended all the way onto the lowland plains (top right). Since the last melting of the glaciers (15,000 years ago) three distinct fan deltas (semicircular features, marked with arrows) have formed where rivers flow into the lake. Counterclockwise currents in the lake-driven by strong winds from the west-have generated thin sand spits from each fan-delta. The largest spit (attached to the largest fan-delta, see right arrow) has isolated an approximately 10-kilometer long segment of the south end of the lake. The river that constructed the largest fan presently discharges turbid water to this isolated basin, giving it a lighter color than the rest of the lake. Glacial data collected over the past 50 years indicate that small ice bodies are disappearing at accelerated rates. (EOS, vol 81, no. 24, June 13, 2000) Predictions are that large fluctuations in land ice, with significant implications to society, are possible in the coming decades and centuries due to natural and anthropogenic climate change. Before glacial data can be used to address critical problems pertaining to the world's economic and environmental health, more detailed information about such glaciers is needed. Image ISS001-ESC-5113 provided by the Earth Sciences and Image Analysis Laboratory, Johnson Space Center.

  12. Cenozoic building and deformational processes in the North Patagonian Andes

    NASA Astrophysics Data System (ADS)

    Orts, Darío L.; Folguera, Andrés; Giménez, Mario; Ruiz, Francisco; Rojas Vera, Emilio A.; Lince Klinger, Federico

    2015-05-01

    The Oligocene to present evolution of the North Patagonian Andes is analyzed linking geological and geophysical data in order to decipher the deformational processes that acted through time and relate them to basin formation processes. Seismic reflection profiles reveal the shallow structure of the retroarc area where contractional structures, associated with Oligocene to early Miocene inverted extensional depocenters, are partially onlapped by early to late Miocene synorogenic deposits. From the construction of five structural cross sections along the retroarc area between 40° and 43°30‧ S, constrained by surface, gravity and seismic data, a shortening gradient is observed along Andean strike. The highest shortening of 18.7 km (15.34%) is determined near 41°30‧ S coincidentally with maximum mean topographic values on the eastern Andean slope, where basement blocks were uplifted in the orogenic front area, and the deepest and broadest synorogenic depocenters were formed towards the foreland. Additionally, eastward shifting of Miocene calc-alkaline rocks occurred at these latitudes, which is interpreted as indicative of a change in the subduction parameters at this time. Deep crustal retroarc structure is evaluated through inversion of gravity models that made possible to infer Moho attenuated zones. These coincide with the occurrence of younger than 5 Ma within-plate volcanics as well as with crustal thermal anomalies suggested by shallowing of the Curie isotherm calculated from magnetic data. Younger volcanism and thermal anomalies are explained by slab steepening since early Pliocene, after a mild-shallow subduction setting in the middle to late Miocene, age of the main compressive event.

  13. Glacier loss and emerging hydrologic vulnerabilities in the Peruvian Andes

    NASA Astrophysics Data System (ADS)

    Mark, B. G.; McKenzie, J. M.; Baraer, M.; Lagos, P.; Lautz, L.; Carey, M.; Bury, J.; Crumley, R.; Wigmore, O.; Somers, L. D.

    2015-12-01

    Accelerating glacier recession in the tropical Andes is transforming downstream hydrology, while increasing demands for water by end-users (even beyond the watershed limits) is complicating the assessment of vulnerability. Future scenarios of hydro-climatic vulnerability require a better understanding of coupled hydrologic and human systems, involving both multiscale process studies and more robust models of glacier-climate interactions. We synthesize research in two proglacial valleys of glacierized mountain ranges in different regions of Peru that are both in proximity to growing water usage from urban sectors, agriculture, hydroelectric generation, and mining. In both the Santa River watershed draining the Cordillera Blanca and the Shullcas River watershed below Hyuatapallana Mountain in Junin, glaciers have receded over 25% since the 1980s. Historical runoff and glacier data, combined with glacier-climate modeling, show a long-term decrease in discharge resulting from a net loss of stored water. We find evidence that this altered hydrology is transforming proglacial wetland ecology and water quality, even while water resource use has intensified. Beyond glaciers, our results show that over 60% of the dry season base flow in each watershed is groundwater sourced from heterogeneous aquifers. Municipal water supply in Huancayo already relies on 18 groundwater wells. Perceptions of water availability and actual water use practices remain relatively divorced from the actual water resources provided from each mountain range. Critical changes in glacier volume and water supply are not perceived or acknowledged consistently amongst different water users, nor reflected in water management decisions. In order to identify, understand, model, and adapt to climate-glacier-water changes, it is vital to integrate the analysis of water availability and groundwater processes (the domain of hydrologists) with that of water use (the focus for social scientists). Attention must be

  14. High resolution precipitation climatology for the Andes of South Ecuador

    NASA Astrophysics Data System (ADS)

    Trachte, Katja; Bendix, Jörg

    2014-05-01

    The climate of Ecuador is strongly dominated by the complex structure of the Andes Mountains. Due to their heights and north-south orientation they act like a barrier, which cause delineation between the western and eastern flanks, as well as the inner-Andean areas. Commonly the Ecuadorian climate is classified in three zones, Costa, Interandina and Oriente. Existing precipitation products such as the GPCC or TRMM data are enabled to represent these climate zones, but because of their spatial resolution, they pass to capture the different regimes within a zone. Especially the inner-Andean region (Interandina) with its characteristic complex terrain shows spatially high climate variability. Local circulation systems, e.g. mountain-valley breezes as well as effects of windward and lee-side, drive the climate conditions allowing for the differentiation of air temperature and rainfall distribution on relative small scales. These highly variable patterns are also reflected by the diversity of ecosystems, e.g. rainforest, dry forest and Paramo, in a relative small area. In order to represent the local systems a dynamical downscaling approach for the Ecuadorian region is applied. In doing so the Weather Research and Forecasting (WRF) model is used. A suitable model setup was evaluated within a sensitivity study, where various parametrization schemes were tested. The most suitable physics combination was used for a 30 year hint cast simulation. The poster presents first results of the high resolution climate simulations. On the basis of the spatial distribution of rainfall patterns distinct precipitation regimes within the Interandina will be shown. The aim is to highlight and discuss the importance of the adequately representation of the terrain in mountainous regions like the Andean Mountains.

  15. Host mTORC1 Signaling Regulates Andes Virus Replication

    PubMed Central

    McNulty, Shannon; Flint, Mike; Nichol, Stuart T.

    2013-01-01

    Hantavirus pulmonary syndrome (HPS) is a severe respiratory disease characterized by pulmonary edema, with fatality rates of 35 to 45%. Disease occurs following infection with pathogenic New World hantaviruses, such as Andes virus (ANDV), which targets lung microvascular endothelial cells. During replication, the virus scavenges 5′-m7G caps from cellular mRNA to ensure efficient translation of viral proteins by the host cell cap-dependent translation machinery. In cells, the mammalian target of rapamycin (mTOR) regulates the activity of host cap-dependent translation by integrating amino acid, energy, and oxygen availability signals. Since there is no approved pharmacological treatment for HPS, we investigated whether inhibitors of the mTOR pathway could reduce hantavirus infection. Here, we demonstrate that treatment with the FDA-approved rapamycin analogue temsirolimus (CCI-779) blocks ANDV protein expression and virion release but not entry into primary human microvascular endothelial cells. This effect was specific to viral proteins, as temsirolimus treatment did not block host protein synthesis. We confirmed that temsirolimus targeted host mTOR complex 1 (mTORC1) and not a viral protein, as knockdown of mTORC1 and mTORC1 activators but not mTOR complex 2 components reduced ANDV replication. Additionally, primary fibroblasts from a patient with tuberous sclerosis exhibited increased mTORC1 activity and increased ANDV protein expression, which were blocked following temsirolimus treatment. Finally, we show that ANDV glycoprotein Gn colocalized with mTOR and lysosomes in infected cells. Together, these data demonstrate that mTORC1 signaling regulates ANDV replication and suggest that the hantavirus Gn protein may modulate mTOR and lysosomal signaling during infection, thus bypassing the cellular regulation of translation. PMID:23135723

  16. Vernal Point and Seismic Activity in Tibet Mountains and Andes Mountains

    NASA Astrophysics Data System (ADS)

    Chavez-Sumarriva, Israel; Chavez-Campos, Teodosio; Chavez S, Nadia

    2014-05-01

    The gravitational influence of the sun and moon on the equatorial bulges of the mantle of the rotating earth causes the precession of the earth. The retrograde motion of the vernal point through the zodiacal band is 26,000 years and passes through each constellation in an average of 2000 years (Milankovitch subcycle). The vernal point retrogrades one precessional degree approximately in 72 years (Gleissberg-cycle), and approximately enters into the Aquarius constellation (declination 11.5° S) on March 20, 1940. On earth this entry was verify through: a) stability of the magnetic equator in the south central zone of Peru and in the north zone of Bolivia (11.5º South latitude) since 1940 b) the greater intensity of equatorial electrojet (EEJ) in Peru and Bolivia since 1940. Besides, there was a long history of studies of coupling between earthquake-ionosphere. In IUGG (Italy-2007), Cusco was proposed as a prime meridian that was based on: (1) the new prime meridian (72º W == 0º) was parallel to the Andes and its projection the meridian (108° E == 180º) intersects the Tibetan plate (Asia). (2) On earth these two areas present the greatest thickness of the crust with an average depth of 70 kilometers. The aim was to synchronize the earth sciences phenomena (e.g. geology, geophysics, etc.). The coordinate system had the vernal point from meridian (72º W== 0º) and March 20, 1940. The retrograde movement of the vernal point was the first precessional degree (2012 = 1940 + 72). The west coast of South America (parallel to meridian 72º W== 0º) was a segment of the circum-pacific seismic belt where more than two thirds of major earthquakes in the world happened. During the first precessional degree (1940 +72 ==2012) seismic activity were: (a) near the new prime meridian (72° W == 0°) occurs in: (a1) Haiti (18.4° N, 72.5° W), January 12, 2010 with magnitude of 7.0 Mw. (a2) Chile (36.28° S, 73.23° W), February 27, 2010 with Magnitude of 8.8 Mw. (a3) Chile (35

  17. Central effects of fingolimod.

    PubMed

    Cruz, Vítor T; Fonseca, Joaquim

    2014-08-01

    Introduccion. El fingolimod, un modulador del receptor de la esfingosina-1-fosfato (S1P) dotado de un mecanismo de accion novedoso, fue el primer tratamiento oral aprobado para la esclerosis multiple remitente recurrente. Su union a los receptores S1P1 de los linfocitos promueve la retencion selectiva de los linfocitos T virgenes y de memoria central en los tejidos linfoides secundarios, lo que impide su salida hacia el sistema nervioso central (SNC). Asimismo, el fingolimod atraviesa con facilidad la barrera hematoencefalica, y diversos estudios le atribuyen un efecto neuroprotector directo en el SNC. Objetivo. Revisar la informacion disponible acerca de los efectos centrales del fingolimod. Desarrollo. El desequilibrio entre los procesos lesivos y reparadores constituye un reflejo de la desmielinizacion cronica, la degeneracion axonal y la gliosis, y parece contribuir a la discapacidad que la esclerosis multiple acarrea. La facilidad con la que el fingolimod atraviesa la barrera hematoencefalica le permite actuar directamente sobre los receptores S1P localizados en las celulas del SNC. Una vez en el interior del SNC, ocupa los receptores S1P de los oligodendrocitos y de sus celulas precursoras, de los astrocitos, los microgliocitos y las neuronas, fomentando la remielinizacion, la neuroproteccion y los procesos endogenos de regeneracion. La eficacia evidenciada en los ensayos clinicos concuerda con un mecanismo de accion que incluiria efectos directos sobre las celulas del SNC. Conclusiones. Los datos disponibles indican que la eficacia del fingolimod en el tratamiento de la esclerosis multiple se debe a su ambivalencia como molecula inmunomoduladora y moduladora directa de los receptores S1P del SNC. Tanto es asi que estudios recientes le atribuyen efectos neuroprotectores en varios modelos que suscitan expectativas en torno a su posible aplicacion terapeutica en la enfermedad de Alzheimer, el paludismo cerebral y el neuroblastoma, asi como en la neuroproteccion

  18. A remote sensing assessment of the impact of the 2010 Maule, Chile earthquake (Mw 8.8) on the volcanoes of the southern Andes

    NASA Astrophysics Data System (ADS)

    Pritchard, M. E.; Welch, M.; Jay, J.; Button, N.

    2011-12-01

    del Maule and Cordón Caulle (which began a major eruption in June, 2011). The deformation rate at Laguna del Maule continues through 2011 at a similar high rate, accumulating more than 60 cm of vertical deformation since 2007 -- making it one of the largest deformation signals without recent eruption yet observed. The rate of uplift at Laguna del Maule seems to be unchanged before and after the 2010 Maule earthquake. The spatial and temporal deformation at Cordón Caulle is complex as noted by Fournier et al., 2010, but does not appear to have been changed by the Maule earthquake either. The reasons that the 2010 Maule earthquake did not strongly affect the closest volcanic arc in the southern Andes remains a mystery. Comparison with the 2004 Sumatra (Mw 9.2) and the 2011 Japan (Mw 9.0) earthquakes and their closest volcanic arcs could provide clues to the elusive links between large earthquakes and volcanic unrest.

  19. Comment on “Human impacts on headwater fluvial systems in the northern and central Andes” (Carol P. Harden, Geomorphology 79, 249 263)

    NASA Astrophysics Data System (ADS)

    Buytaert, Wouter; De Bièvre, Bert; Celleri, Rolando; Cisneros, Felipe; Wyseure, Guido; Deckers, Seppe

    2008-04-01

    The high altitude grasslands of the tropical Andes, known as páramo, are a very fragile and unique ecosystem. Despite increasing human activities, many of its geomorphological and hydrological processes are still very poorly understood. We therefore welcome the paper of Harden [Harden, C.P., 2006. Human impacts on headwater fluvial systems in the northern and central Andes. Geomorphology 79, 249-263.] about "Human impacts on headwater fluvial systems in the northern and central Andes" as a valuable contribution to a better understanding of this complex ecosystem. However, in view of the available literature, we would like to complement the interpretation of the presented results and discuss some of the claims made in the paper.

  20. Hybrid Literacies: The Case of a Quechua Community in the Andes

    ERIC Educational Resources Information Center

    de la Piedra, Maria Teresa

    2009-01-01

    Drawing on data from an ethnographic study in a Quechua rural community in the Peruvian Andes, this article examines hybrid literacy practices among bilingual rural speakers in the context of the household and the community. I examine the coexistence of two types of textual practices that operate side by side, at times integrated in the same…

  1. Lichenometric dating using Rhizocarpon subgenus Rhizocarpon in the Patagonian Andes, Argentina

    NASA Astrophysics Data System (ADS)

    Garibotti, Irene Adriana; Villalba, Ricardo

    2009-05-01

    This study represents the first attempt to develop and apply lichenometric dating curves of Rhizocarpon subgenus Rhizocarpon for dating glacier fluctuations in the Patagonian Andes. Six glaciers were studied along the Patagonian Andes. Surfaces of known ages (historical evidences and tree-ring analyses) were used as control sites to develop indirect lichenometric dating curves. Dating curves developed for the studied glaciers show the same general logarithmic form, indicating that growth rate of subgenus Rhizocarpon decreases over time. The strong west-east precipitation gradient across the Andean Cordillera introduces statistically significant differences in the growth curves, with faster growth rates in the moist west sites than the drier eastern sites. Latitudinal difference among the studied glaciers does not appear to be a major factor regulating lichen growth rates. Therefore, we developed two lichenometric curves for dating glacier fluctuations in wetter and drier sites in the Patagonian Andes during the past 450 yrs. Application of the developed curves to moraine dating allowed us to complement glacial chronologies previously obtained by tree-ring analyses. A first chronosequence for moraine formation in the Torrecillas Glacier (42°S) is presented. Our findings confirm the utility of lichenometry to date deglaciated surfaces in the Patagonian Andes.

  2. Knowledge and Learning in the Andes: Ethnographic Perspectives. Liverpool Latin American Studies, New Series 3.

    ERIC Educational Resources Information Center

    Stobart, Henry, Ed.; Howard, Rosaleen, Ed.

    This book presents research into the ways in which Indigenous peoples of the Andes create, transmit, maintain, and transform their knowledge, and the related processes of teaching and learning. Most chapters are based on papers delivered at a round-table conference at the University of Cambridge (England) in 1996 and include contributions from…

  3. "Nervios" and "Modern Childhood": Migration and Shifting Contexts of Child Life in the Ecuadorian Andes.

    ERIC Educational Resources Information Center

    Pribilsky, Jason

    2001-01-01

    Argues that beyond explanations predicated on psychological ideas of separation and attachment, "nervios," a depression-like disorder among children in the southern Ecuadorian Andes, reflects the limits of children's abilities to accept terms of family life increasingly defined through transnational migration and new consumption practices.…

  4. New host and lineage diversity of avian haemosporidia in the northern Andes

    PubMed Central

    Harrigan, Ryan J; Sedano, Raul; Chasar, Anthony C; Chaves, Jaime A; Nguyen, Jennifer T; Whitaker, Alexis; Smith, Thomas B

    2014-01-01

    The northern Andes, with their steep elevational and climate gradients, are home to an exceptional diversity of flora and fauna, particularly rich in avian species that have adapted to divergent ecological conditions. With this diversity comes the opportunity for parasites to exploit a wide breadth of avian hosts. However, little research has focused on examining the patterns of prevalence and lineage diversity of avian parasites in the Andes. Here, we screened a total of 428 birds from 19 species (representing nine families) and identified 133 infections of avian haemosporidia (31%), including lineages of Plasmodium, Haemoproteus, and Leucocytozoon. We document a higher prevalence of haemosporidia at higher elevations and lower temperatures, as well as an overall high diversity of lineages in the northern Andes, including the first sequences of haemosporidians reported in hummingbirds (31 sequences found in 11 species within the family Trochilidae). Double infections were distinguished using PHASE, which enables the separation of distinct parasite lineages. Results suggest that the ecological heterogeneity of the northern Andes that has given rise to a rich diversity of avian hosts may also be particularly conducive to parasite diversification and specialization. PMID:25469161

  5. Subduction of the South Chile active spreading ridge: A 17 Ma to 3 Ma magmatic record in central Patagonia (western edge of Meseta del Lago Buenos Aires, Argentina)

    NASA Astrophysics Data System (ADS)

    Boutonnet, E.; Arnaud, N.; Guivel, C.; Lagabrielle, Y.; Scalabrino, B.; Espinoza, F.

    2010-01-01

    The Chile Triple Junction is a natural laboratory to study the interactions between magmatism and tectonics during the subduction of an active spreading ridge beneath a continent. The MLBA plateau (Meseta del Lago Buenos Aires) is one of the Neogene alkali basaltic plateaus located in the back-arc region of the Andean Cordillera at the latitude of the current Chile Triple Junction. The genesis of MLBA can be related with successive opening of slabs windows beneath Patagonia: within the subducting Nazca Plate itself and between the Nazca and Antarctic plates. Detailed 40Ar/ 39Ar dating and geochemical analysis of bimodal magmatism from the western flank of the MLBA show major changes in the back-arc magmatism which occurred between 14.5 Ma and 12.5 Ma with the transition from calc-alkaline lavas (Cerro Plomo) to alkaline lavas (MLBA) in relation with slab window opening. In a second step, at 4-3 Ma, alkaline felsic intrusions were emplaced in the western flank of the MLBA coevally with the MLBA basalts with which they are genetically related. These late OIB-like alkaline to transitional basalts were generated by partial melting of the subslab asthenosphere of the subducting Nazca plate during the opening of the South Chile spreading ridge-related slab window. These basalts differentiated with small amounts of assimilation in shallow magma chambers emplaced along transtensional to extensional zones. The close association of bimodal magmatism with extensional tectonic features in the western MLBA is a strong support to the model of Patagonian collapse event proposed to have taken place between 5 and 3 Ma as a consequence of the presence of the asthenospheric window (SCR-1 segment of South Chile Ridge) below the MLBA area.

  6. Paleoecological potential of mid-altitude peat deposits in the Tropical Andes: evidence from subfossil wood and palynology

    NASA Astrophysics Data System (ADS)

    Gonzalez Arango, Catalina; Andres Ayala Usma, David; Boom, Arnoud; Archila, Sonia; Montes, Camilo

    2016-04-01

    The understanding of past climatic and ecological phenomena at mid-altitudes in the tropical Andes is limited by the lack of ancient lakes and other well preserved paleoclimatological archives. During the opening of a main road a decade ago in the Central Cordillera of Colombia, some buried peat deposits became exposed within the Pereira Volcanodetritic Fan (~2000 m.a.s.l), revealing a rich resource of organic remains, including big fragments of subfossil trees and micro and macro plant remains ideal for multiproxy analysis. Radiocarbon dating and palynological analysis suggest that the deposit dates back to the last glacial period. We present the first δ13C results of a subfossil wood sample with visible tree rings, that was identified as a member of the genus Chrysochlamys (Clusiaceae) and that revealed a periodic signal that might be attributed to climatic variability. A clear seasonal pattern arises suggesting a different climatic configuration, most likely related to a broader migrational range of the ITCZ related to higher eccentricity. Pollen analysis reveals the prevalence of montane Andean forests and Paramo elements (today ca. 1200 meters higher) indicating much colder climates than today. These first findings indicate that mid-altitude Andean peats are highly sensitive to climatic variability and provide an excellent opportunity to study ancient environmental phenomena at extremely high resolution.

  7. The role of the Antofagasta-Calama Lineament in ore deposit deformation in the Andes of northern Chile

    NASA Astrophysics Data System (ADS)

    Palacios, Carlos; Ramírez, Luis E.; Townley, Brian; Solari, Marcelo; Guerra, Nelson

    2007-02-01

    During the Late Jurassic-Early Oligocene interval, widespread hydrothermal copper mineralization events occurred in association with the geological evolution of the southern segment of the central Andes, giving rise to four NS-trending metallogenic belts of eastward-decreasing age: Late Jurassic, Early Cretaceous, Late Paleocene-Early Eocene, and Late Eocene-Early Oligocene. The Antofagasta-Calama Lineament (ACL) consists of an important dextral strike-slip NE-trending fault system. Deformation along the ACL system is evidenced by a right-lateral displacement of the Late Paleocene-Early Eocene metallogenic belts. Furthermore, clockwise rotation of the Early Cretaceous Mantos Blancos copper deposit and the Late Paleocene Lomas Bayas porphyry copper occurred. In the Late Eocene-Early Oligocene metallogenic belt, a sigmoidal deflection and a clockwise rotation is observed in the ACL. The ACL is thought to have controlled the emplacement of Early Oligocene porphyry copper deposits (34-37 Ma; Toki, Genoveva, Quetena, and Opache), whereas it deflected the Late Eocene porphyry copper belt (41-44 Ma; Esperanza, Telégrafo, Centinela, and Polo Sur ore deposits). These observations suggest that right-lateral displacement of the ACL was active during the Early Oligocene. We propose that the described structural features need to be considered in future exploration programs within this extensively gravel-covered region of northern Chile.

  8. New dinosaur (Theropoda, stem-Averostra) from the earliest Jurassic of the La Quinta formation, Venezuelan Andes.

    PubMed

    Langer, Max C; Rincón, Ascanio D; Ramezani, Jahandar; Solórzano, Andrés; Rauhut, Oliver W M

    2014-10-01

    Dinosaur skeletal remains are almost unknown from northern South America. One of the few exceptions comes from a small outcrop in the northernmost extension of the Andes, along the western border of Venezuela, where strata of the La Quinta Formation have yielded the ornithischian Laquintasaura venezuelae and other dinosaur remains. Here, we report isolated bones (ischium and tibia) of a small new theropod, Tachiraptor admirabilis gen. et sp. nov., which differs from all previously known members of the group by an unique suite of features of its tibial articulations. Comparative/phylogenetic studies place the new form as the sister taxon to Averostra, a theropod group that is known primarily from the Middle Jurassic onwards. A new U-Pb zircon date (isotope dilution thermal-ionization mass spectrometry; ID-TIMS method) from the bone bed matrix suggests an earliest Jurassic maximum age for the La Quinta Formation. A dispersal-vicariance analysis suggests that such a stratigraphic gap is more likely to be filled by new records from north and central Pangaea than from southern areas. Indeed, our data show that the sampled summer-wet equatorial belt, which yielded the new taxon, played a pivotal role in theropod evolution across the Triassic-Jurassic boundary. PMID:26064540

  9. New dinosaur (Theropoda, stem-Averostra) from the earliest Jurassic of the La Quinta formation, Venezuelan Andes.

    PubMed

    Langer, Max C; Rincón, Ascanio D; Ramezani, Jahandar; Solórzano, Andrés; Rauhut, Oliver W M

    2014-10-01

    Dinosaur skeletal remains are almost unknown from northern South America. One of the few exceptions comes from a small outcrop in the northernmost extension of the Andes, along the western border of Venezuela, where strata of the La Quinta Formation have yielded the ornithischian Laquintasaura venezuelae and other dinosaur remains. Here, we report isolated bones (ischium and tibia) of a small new theropod, Tachiraptor admirabilis gen. et sp. nov., which differs from all previously known members of the group by an unique suite of features of its tibial articulations. Comparative/phylogenetic studies place the new form as the sister taxon to Averostra, a theropod group that is known primarily from the Middle Jurassic onwards. A new U-Pb zircon date (isotope dilution thermal-ionization mass spectrometry; ID-TIMS method) from the bone bed matrix suggests an earliest Jurassic maximum age for the La Quinta Formation. A dispersal-vicariance analysis suggests that such a stratigraphic gap is more likely to be filled by new records from north and central Pangaea than from southern areas. Indeed, our data show that the sampled summer-wet equatorial belt, which yielded the new taxon, played a pivotal role in theropod evolution across the Triassic-Jurassic boundary.

  10. New dinosaur (Theropoda, stem-Averostra) from the earliest Jurassic of the La Quinta formation, Venezuelan Andes

    PubMed Central

    Langer, Max C.; Rincón, Ascanio D.; Ramezani, Jahandar; Solórzano, Andrés; Rauhut, Oliver W. M.

    2014-01-01

    Dinosaur skeletal remains are almost unknown from northern South America. One of the few exceptions comes from a small outcrop in the northernmost extension of the Andes, along the western border of Venezuela, where strata of the La Quinta Formation have yielded the ornithischian Laquintasaura venezuelae and other dinosaur remains. Here, we report isolated bones (ischium and tibia) of a small new theropod, Tachiraptor admirabilis gen. et sp. nov., which differs from all previously known members of the group by an unique suite of features of its tibial articulations. Comparative/phylogenetic studies place the new form as the sister taxon to Averostra, a theropod group that is known primarily from the Middle Jurassic onwards. A new U–Pb zircon date (isotope dilution thermal-ionization mass spectrometry; ID-TIMS method) from the bone bed matrix suggests an earliest Jurassic maximum age for the La Quinta Formation. A dispersal–vicariance analysis suggests that such a stratigraphic gap is more likely to be filled by new records from north and central Pangaea than from southern areas. Indeed, our data show that the sampled summer-wet equatorial belt, which yielded the new taxon, played a pivotal role in theropod evolution across the Triassic–Jurassic boundary. PMID:26064540

  11. The effect of highly variable topography on the spatial distribution of Aniba perutilis (Lauraceae) in the Colombian Andes.

    PubMed

    Fagua, JoséC; Cabrera, Edersson; Gonzalez, Victor H

    2013-03-01

    Topography is a factor that can significantly affect the diversity and the distribution of trees species in tropical forests. Aniba perutilis, a timber species listed as vulnerable to extinction, is widely distributed in Andean forest fragments, especially in those with highly variable topography. Based on field surveys and logistic regression analyses, we studied the population structure and the effect of highly variable topography on the spatial distribution of this tree in three protected forest fragments in the central Andes of Colombia. Individuals of A. perutilis were mainly found on mountain ridges and hills with gentle slopes; no individuals were found in valleys. Using a species distribution model with presence/absence data, we showed that the available habitat for A. perutilis is significantly smaller than the extension of the fragments and much smaller than the extension of the currently protected areas. Our results have important implications for the conservation ofA. perutilis and likely for other threatened Andean tree species, which can also have locally restricted distributions due to highly variable local topography.

  12. Water and sediment quality of the Lake Andes and Choteau Creek basins, South Dakota, 1983-2000

    USGS Publications Warehouse

    Sando, Steven Kent; Neitzert, Kathleen M.

    2003-01-01

    The Bureau of Reclamation has proposed construction of the Lake Andes/Wagner Irrigation Demonstration Project to investigate environmental effects of irrigation of glacial till soils substantially derived from marine shales. During 1983-2000, the U.S. Geological Survey collected hydrologic, water-quality, and sediment data in the Lake Andes and Choteau Creek Basins, and on the Missouri River upstream and downstream from Choteau Creek, to provide baseline information in support of the proposed demonstration project. Lake Andes has a drainage area of about 230 mi2 (square miles). Tributaries to Lake Andes are ephemeral. Water-level fluctuations in Lake Andes can be large, and the lake has been completely dry on several occasions. The outlet aqueduct from Lake Andes feeds into Garden Creek, which enters Lake Francis Case just upstream from Fort Randall Dam on the Missouri River. For Lake Andes tributary stations, calcium, magnesium, and sodium are approximately codominant among the cations, and sulfate is the dominant anion. Dissolved-solids concentrations typically range from about 1,000 mg/L (milligrams per liter) to about 1,700 mg/L. Major-ion concentrations for Lake Andes tend to be higher than the tributaries and generally increase downstream in Lake Andes. Proportions of major ions are similar among the different lake units (with the exception of Owens Bay), with calcium, magnesium, and sodium being approximately codominant among cations, and sulfate being the dominant anion. Owens Bay is characterized by a calcium sulfate water type. Dissolved-solids concentrations for Lake Andes typically range from about 1,400 to 2,000 mg/L. Whole-water nitrogen and phosphorus concentrations are similar among the Lake Andes tributaries, with median whole-water nitrogen concentrations ranging from about 1.6 to 2.4 mg/L, and median whole-water phosphorus concentrations ranging from about 0.5 to 0.7 mg/L. Whole-water nitrogen concentrations in Lake Andes are similar among the

  13. A high-altitude peatland record of environmental changes in the NW Argentine Andes (24 ° S) over the last 2100 years

    NASA Astrophysics Data System (ADS)

    Schittek, Karsten; Kock, Sebastian T.; Lücke, Andreas; Hense, Jonathan; Ohlendorf, Christian; Kulemeyer, Julio J.; Lupo, Liliana C.; Schäbitz, Frank

    2016-05-01

    High-altitude cushion peatlands are versatile archives for high-resolution palaeoenvironmental studies, due to their high accumulation rates, range of proxies, and sensitivity to climatic and/or human-induced changes. Especially within the Central Andes, the knowledge about climate conditions during the Holocene is limited. In this study, we present the environmental and climatic history for the last 2100 years of Cerro Tuzgle peatland (CTP), located in the dry Puna of NW Argentina, based on a multi-proxy approach. X-ray fluorescence (XRF), stable isotope and element content analyses (δ13C, δ15N, TN and TOC) were conducted to analyse the inorganic geochemistry throughout the sequence, revealing changes in the peatlands' past redox conditions. Pollen assemblages give an insight into substantial environmental changes on a regional scale. The palaeoclimate varied significantly during the last 2100 years. The results reflect prominent late Holocene climate anomalies and provide evidence that in situ moisture changes were coupled to the migration of the Intertropical Convergence Zone (ITCZ). A period of sustained dry conditions prevailed from around 150 BC to around AD 150. A more humid phase dominated between AD 200 and AD 550. Afterwards, the climate was characterised by changes between drier and wetter conditions, with droughts at around AD 650-800 and AD 1000-1100. Volcanic forcing at the beginning of the 19th century (1815 Tambora eruption) seems to have had an impact on climatic settings in the Central Andes. In the past, the peatland recovered from climatic perturbations. Today, CTP is heavily degraded by human interventions, and the peat deposit is becoming increasingly susceptible to erosion and incision.

  14. Evolution of the Chos Malal and Agrio fold and thrust belts, Andes of Neuquén: Insights from structural analysis and apatite fission track dating

    NASA Astrophysics Data System (ADS)

    Rojas Vera, E. A.; Mescua, J.; Folguera, A.; Becker, T. P.; Sagripanti, L.; Fennell, L.; Orts, D.; Ramos, V. A.

    2015-12-01

    The Chos Malal and Agrio fold and thrust belts are located in the western part of the Neuquén basin, an Andean retroarc basin of central-western Argentina. Both belts show evidence of tectonic inversion at the western part during Late Cretaceous times. The eastern part is dominated by late Miocene deformation which also partially reactivated the western structures. This work focuses on the study of the regional structure and the deformational event that shaped the relief of this part of the Andes. Based on new field work and structural data and previously published works a detailed map of the central part of the Neuquén basin is presented. Three regional structural cross sections were surveyed and balanced using the 2d Move™ software. In order to define a more accurate uplift history, new apatite fission track analyses were carried on selected structures. These data was used for new thermal history modeling of the inner part of the Agrio and Chos Malal fold and thrust belts. The results of the fission track analyses improve the knowledge of how these fold and thrust belts have grown trough time. Two main deformational events are defined in Late Cretaceous to Paleocene and Late Miocene times. Based on this regional structural analysis and the fission track data the precise location of the orogenic front for the Late Cretaceous-Paleocene times is reconstructed and it is proposed a structural evolution of this segment of the Andes. This new exhumation data show how the Late Cretaceous to Paleocene event was a continuous and uninterrupted deformational event.

  15. Utility of multiple chemical techniques in archaeological residential mobility studies: case studies from Tiwanaku- and Chiribaya-affiliated sites in the Andes.

    PubMed

    Knudson, Kelly J; Price, T Douglas

    2007-01-01

    In the south central Andes, archaeologists have long debated the extent of Tiwanaku colonization during the Middle Horizon (AD 500-1000). We tested the hypotheses regarding the nature of Tiwanaku influence using strontium isotope, trace element concentration, and oxygen isotope data from archaeological human tooth enamel and bone from Tiwanaku- and Chiribaya-affiliated sites in the south central Andes. Strontium isotope analysis of 25 individuals buried at the Tiwanaku-affiliated Moquegua Valley site of Chen Chen demonstrates that it was likely a Tiwanaku colony. In contrast, no immigrants from the Lake Titicaca Basin were present in 27 individuals analyzed from the San Pedro de Atacama cemeteries of Coyo Oriental, Coyo-3, and Solcor-3; it is likely that these sites represent economic and religious alliances, but not colonies. However, strontium isotope analysis alone cannot distinguish movement between the Tiwanaku- and Chiribaya-affiliated sites in the Moquegua and Ilo Valleys of southern Peru. Analyzing oxygen isotope and trace element concentration data and comparing it with strontium isotope data from the same individuals provides a more detailed picture of residential mobility in the Tiwanaku and Chiribaya polities. In addition to monitoring diagenetic contamination, trace element concentration data identified movement during adulthood for certain individuals. However, these data could not distinguish movement between the Moquegua and Ilo Valleys. While oxygen isotope data could clearly distinguish the high-altitude sites from others, more data is needed to characterize the local oxygen isotope ratios of these regions. These data demonstrate the potential for archaeological reconstruction of residential mobility through multiple lines of evidence. PMID:17063464

  16. Adapting to Uncertain Futures: Glacier Recession and Livelihood Vulnerability in the Peruvian Andes

    NASA Astrophysics Data System (ADS)

    Bury, J.

    2008-12-01

    With a large portion of the world's population dependent on hydrologic resources linked to tropical glaciers, the decline of these natural "water towers" has important repercussions for the social and ecological systems that depend on these vital reservoirs of freshwater. In Peru's Cordillera Blanca (the highest and most extensively glaciated range in the tropics) glacial melt water makes up a critical percentage of the discharge of a wide array of water courses, ranging from first-order, highland streams to the Rio Santa, one of the largest and most economically important rivers on Peru's Pacific slope. Climate change-induced warming is occurring rapidly in this region and glaciers have lost a significant percentage of their mass in the past 50 years. While there have been indications that significant and temporary increases in glacial meltwater discharge flows will take place, predictions for the coming decades suggest that these flows will decrease and be more variable across seasons in even the most glaciated catchments of the range. Current population levels and patterns of water use in the Central Andes suggest that many human communities are highly vulnerable to decreasing or variable quantities of water and other changes associated with climate change. Here will be presented the first results from two years of field work assessing human vulnerability to increasing hydrological variability due to glacier-recession and evaluating how changing access to water resources is contributing to livelihood adaptation and potential conflicts over resources in the Cordillera Blanca region of Peru. The findings are drawn from stratified case-study research in two communities and are comprised of an extensive set of key interviews with national, regional and local key informants and semi-structured household surveys that were sampled utilizing stratified systematic unaligned techniques. The results provide insights into key elements of household vulnerability, how

  17. Chemical Mineralogy, Geochemical Characterization and Petrography of the Cambumbia Stock, Northern Andes, South America, Colombia

    NASA Astrophysics Data System (ADS)

    Rojas Lequerica, Salvador; María Jaramillo Mejía, José; Concha Perdomo, Ana Elena; Jimenez Quintero, Camilo

    2013-04-01

    The Cambumbia Stock is located on the western flank of the Central Cordillera of the northern Andes, South America. The goals of this study were to characterize the mineral chemistry, the geochemical composition and the petrography of the Cambumbia igneous body and to establish its petrogenesis. We collected 41 samples, selected 28 for thin section petrographic analysis, 14 for whole rock elementary chemical determination by ICP-MS and 4 for chemical mineralogy by LA-ICP(JEOL JXA-8200). Petrographically the samples were classified as 30 % hornblende-gabbro, 30% pyroxene-gabbros, 10% diorites, 10% olivine-gabbro, 7% gabbronorites, 7% tonalities and 3% norite, 3% wehrlite, the rock varies from medium to coarse hipidiomorfic and holocristaline texture, with local microporfiritic texture. Spot elemental chemical analysis of the some minerals in 4 samples show the range of the major elemental composition is plagioclase (labradorite), clinopyroxene (augite), horblende (magnesiohornblende), olivine (fayalite())Chemical mineralogy shows the variety of minerals in this rock, essential minerals correspond to bytownite, augite, magnesio-honblende, fallaite and titanite. We conclude base on the SiO2 Vs Total Alkalis graph that the samples correspond to the sub-alkaline series with low K content, mainly in the calc-alkaline series. By using the SiO2 vs TiO2, Th/Yb vs Ta/Yb and Zr/117-Th-Nb/16 diagrams it was determined that these rocks were generated in two geotectonic environments: one type MOR (extension) and other island arc (subduction, compression). Recently, a U/Pb age was obtained by the Universidad de Caldas in zircon in 2009 (not published data), yielded an age of 233.41 ± 3.4 Ma (Carnian - Upper Triassic). Petrographic geochemical and geochronology comparisons between the rocks of Cambumbia Stock and Diorite and Gabbro El Pueblito (located about 25 km to the north-west) and with U/Pb age 231 ± 8 may postulate a possible genetic link between them. These ages are