Seasonal moisture sources and the isotopic composition of precipitation, rivers, and carbonates across the Andes at 32º-35.5°S

Constraining the influence of different moisture sources across the flanks of mountain ranges is important for understanding tectonic, geomorphic, and paleoclimate problems at geologic timescales, as well as evaluating climate change and water resources on human time scales. The stable isotope compositions of stream waters and precipitation are an ideal tool for this task. This study reports the results of a 2 year monthly precipitation sampling campaign on the eastern flank of the Andes in the Mendoza Province of Argentina, which began in September 2008. A total of 104 precipitation samples spanning some 2500 m of relief from nine sites were analyzed for δD and δ18O. In addition, 81 samples from Andean rivers collected on both sides of the range in 2002 and 2007 were analyzed. We employ a Rayleigh isotope fractionation modeling approach to explore spatial and temporal variations in precipitation and river water compositions. The results indicate that precipitation on the eastern slopes of the Andes at ~33°S, at elevations above 2 km, is largely derived from a westerly, Pacific-source component and a mixture of easterly and westerly sources below 2 km. Further south at ~35°S, river water compositions exhibit a strong winter influence. At 33°S, rivers have an isotopic minimum of ~ −18? across the core of the range, which has an average elevation of 4000 m, and are topographically offset from similar isotopic values of precipitation by +1000 m. Comparison of precipitation and river water data with temperature-corrected δ18O estimates from pedogenic carbonates illustrates that carbonates capture the range of variability observed in modern precipitation and Rayleigh fractionation models.Fil: Hoke, Gregory D.. Syracuse University. Department of Earth Sciences; Estados UnidosFil: Aranibar, Julieta Nelida. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Viale, Maximiliano. Universidad de Chile. Departamento de Geofísica. Facultad de Ciencias Físicas y Matemáticas; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Araneo, Diego Christian. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Llano, Carina. Museo de Historia Natural de San Rafael. Departamento de Antropología; Argentin

Thrust belts of the southern Central Andes: Along-strike variations in shortening, topography, crustal geometry, and denudation

The Andean fold-and-thrust belts of westcentral Argentina (33 S and 36 S), above the normal subduction segment, present important along-strike variations in mean topographic uplift, structural elevation, amount and rate of shortening, and crustal root geometry. To analyze the controlling factors of these latitudinal changes, we compare these parameters and the chronology of deformation along 11 balanced crustal cross sections across the thrust belts between 70 W and 69 W, where the majority of the uppercrustal deformation is concentrated, and reconstruct the Moho geometry along the transects. We propose two models of crustal deformation: a 33 40 S model, where the locus of upper-crustal shortening is aligned with respect to the maximum crustal thickness, and a 35 40 S model, where the uppercrustal shortening is uncoupled from the lower-crustal deformation and thickening. This degree of coupling between brittle upper crust and ductile lower crust deformation has strong influence on mean topographic ele vation. In the northern sector of the study area, an initial thick and felsic crust favors the coupling model, while in the southern sector, a thin and mafic lower crust allows the uncoupling model. Our results indicate that interplate dynamics may control the overall pattern of tectonic shortening; however, local variations in mean topographic elevation, deformation styles, and crustal root geometry are not fully explained and are more likely to be due to upper-plate lithospheric strength variations.Fil: Giambiagi, Laura Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Mescua, Jose Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Bechis, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio. Universidad Nacional de Río Negro. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio; ArgentinaFil: Tassara Oddo, Andres Humberto. Universidad de Concepción; ChileFil: Hoke, Gregory D.. Syracuse University; Estados Unido

Sedimentologic and stratigraphic evolution of the Cacheuta basin: Constraints on the development of the Miocene retroarc foreland basin, south-central Andes

Retroarc foreland basins in contractional arc settings contain evidence of temporal and spatial variations in magmatic activity, deformation, and exhumation along the continental margin and serve as excellent recorders of subduction dynamics through time. The Cacheuta basin, northwestern Mendoza Province, Argentina, is situated within the transition zone between the Pampean flat-slab subduction segment north of 33°S and the normal-dipping slab segment of the Southern Volcanic Zone to the south, and it records a detailed history of Andean orogenic exhumation at this latitude. The integration of sedimentologic, stratigraphic, geochronologic, and sediment provenance data from the Cacheuta basin constrains orogenic exhumation patterns and basin evolution during basin development. Cacheuta basin strata record at least a 12 m.y. period of basin evolution (ca. 20 Ma to younger than 7.5 Ma), based on new geochronology. The timing of initial basin subsidence is constrained by the lowermost sample in the Mariño Formation, which yielded a maximum depositional age of 19.2 ± 0.26 Ma, ∼4 m.y. earlier than previous interpretations. Conglomerate clast counts, thin section petrography, and detrital zircon analyses, coupled with distinct sedimentologic variations, record progressive orogenic exhumation of the Cordillera Principal, Cordillera Frontal, and Precordillera during early to middle Miocene time. Examination of basinal strata demonstrate that uplift of the Cordillera Principal, Cordillera Frontal, and Precordillera, and simultaneous development of the Cacheuta retroarc foreland basin, in the early to mid-Miocene was the result of contractional deformation and crustal thickening during normal subduction-related orogenic processes and did not result from the development of the flat slab in late Miocene time.Fil: Buelow, E. K.. University of Wisconsin; Estados UnidosFil: Suriano, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Mahoney, J. B.. University of Wisconsin; Estados UnidosFil: Kimbrough, D. L.. San Diego State University; Estados UnidosFil: Mescua, Jose Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Giambiagi, Laura Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Hoke, Gregory D.. Syracuse University; Estados Unido

Rise of the Andes

The surface uplift of mountain belts is generally assumed to reflect progressive shortening and crustal thickening, leading to their gradual rise. Recent studies of the Andes indicate that their elevation remained relatively stable for long periods (tens of millions of years), separated by rapid (1 to 4 million years) changes of 1.5 kilometers or more. Periodic punctuated surface uplift of mountain belts probably reflects the rapid removal of unstable, dense lower lithosphere after long-term thickening of the crust and lithospheric mantle

Detrital Thermochronology Reveals Major Middle Miocene Exhumation of the Eastern Flank ofthe Andes That Predates the PampeanFlat Slab (33°–33.5°S)

The Cordón del Plata and Cordón del Portillo (32.6°?33.8°S) are the portions of the FrontalCordillera that straddle the transition zone between the Pampean flat‐slab subduction segment to thenorth and the normal subduction segment to the south. A complete understanding of how the FrontalCordillera developed is necessary in order to evaluate different tectonic models for the Andes along withtheir relation to subduction dynamics and contractional upper‐crustal deformation. Detrital apatite fissiontrack thermochronology of modern river sediments that drain the eastern and western slopes of theCordón del Plata and the northern Cordón del Portillo provides constraints on regional exhumationhistories. AFT data from each catchment typically contain multiple age peaks, but all have a prominent15.3?17 Ma age peak. One catchment, the Las Tunas River has a unimodal distribution at 17.0 ± 1.1 Ma, with a confined track length distribution indicative of rapid cooling at that time. These results, combined with provenance analysis in the adjacent Cacheuta Basin, indicate significant early to middle Miocene (~16 Ma) exhumation in the Cordón del Plata and the northern sector of the Cordón del Portillo. Exhumation related to rock uplift occurred prior to the ~11 Ma onset of a flat slab eometry at these latitudes, but immediately after the main east vergent contractional event in the adjacent Principal Cordillera. Such Frontal Cordillera exhumation fits in an eastward, youngest to the foreland sequence of deformation of the different morphostructural Andean units at ~33°?34°S, arguing against the recently proposed west vergent orogenic system at these latitudes.Fil: Lossada, Ana Clara. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; ArgentinaFil: Hoke, Gregory D.. Syracuse University. College Of Arts And Sciences. Department Of Earth Sciences; Estados UnidosFil: Giambiagi, Laura Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Fitzgerald, P. G.. Syracuse University. College Of Arts And Sciences. Department Of Earth Sciences; Estados UnidosFil: Mescua, Jose Francisco. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Suriano, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Aguilar, A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Dating the incision of the Yangtze River gorge at the First Bend using three-nuclide burial ages

Incision of the Yangtze River gorge is widely interpreted as evidence for lower crustal flow beneath the southeast margin of the Tibetan Plateau. Previous work focused on the onset of incision, but the duration of incision remains unknown. Here we present cosmogenic nuclide burial ages of sediments collected from caves on the walls of the gorge that show the gorge was incised ~1 km sometime between 18 and 9 Ma. Thereafter, incision slowed substantially. We resolve middle Miocene burial ages by using three nuclides and accounting for in situ muogenic production. This approach explains the absolute concentrations of 10Be, 26Al, and 21Ne, as well as 26Al/10Be and 21Ne/10Be ratios. A declining incision rate challenges existing geodynamic interpretations by suggesting that either (1) surface uplift has ceased immediately south of the plateau margin or (2) gorge incision is not a useful proxy for the timing of surface uplift

Erosion rate maps highlight spatio-temporal patterns of uplift and quantify sediment export of the Northern Andes

Erosion rates are widely used to assess tectonic uplift and sediment export from mountain ranges. However, the scarcity of erosion rate measurements often hinders detailed tectonic interpretations. Here, we present 25 new cosmogenic nuclide-derived erosion rates from the Northern Andes of Colombia to study spatio-temporal patterns of uplift along the Central and Eastern Cordillera. Specifically, we combine new and published erosion rate data with precipitation-corrected normalized channel steepness measurements to construct high-resolution erosion rate maps. We find that erosion rates in the southern Central Cordillera are relatively uniform and average ∼0.3 mm/a. In the northern Central Cordillera rapidly eroding canyons dissect slowly eroding, low-relief surfaces uplifting since 8.3+ 3.7 - 2.6 Ma, based on a block uplift model. We interpret that persistent steep slab subduction has led to an erosional steady-state in the southern Central Cordillera, whereas in the northern Central Cordillera, Late Miocene slab flattening caused an acceleration in uplift, to which the landscape has not yet equilibrated. The Eastern Cordillera also displays pronounced erosional disequilibrium, with a slowly eroding central plateau rimmed by faster eroding western and eastern flanks. Our maps suggest Late Miocene topographic growth of the Eastern Cordillera, with deformation focused along the eastern flank, which is also supported by balanced cross-sections and thermochronologic data. Spatial gradients in predicted erosion rates along the eastern flank of the Eastern Cordillera suggest transient basin-ward migration of thrusts. Finally, sediment fluxes based on our erosion maps, suggest that the Eastern Cordillera exports nearly four times more sediment than the Central Cordillera. Our analysis shows that accounting for spatial variations in erosion parameters and climate reveals important variations in tectonic forcing that would otherwise be obscured in traditional river profile analyses. Moreover, given relationships between tectonic and topographic evolution, we hypothesize that spatio-temporal variations in slab dip are the primary driver of the dynamic landscape evolution of the Northern Andes, with potentially superposed effects from inherited Mesozoic rift structures

Mutational analysis of the C-terminal FATC domain of Saccharomyces cerevisiae Tra1

Tra1 is a component of the Saccharomyces cerevisiae SAGA and NuA4 complexes and a member of the PIKK family, which contain a C-terminal phosphatidylinositol 3-kinase-like (PI3K) domain followed by a 35-residue FATC domain. Single residue changes of L3733A and F3744A, within the FATC domain, resulted in transcriptional changes and phenotypes that were similar but not identical to those caused by mutations in the PI3K domain or deletions of other SAGA or NuA4 components. The distinct nature of the FATC mutations was also apparent from the additive effect of tra1-L3733A with SAGA, NuA4, and tra1 PI3K domain mutations. Tra1-L3733A associates with SAGA and NuA4 components and with the Gal4 activation domain, to the same extent as wild-type Tra1; however, steady-state levels of Tra1-L3733A were reduced. We suggest that decreased stability of Tra1-L3733A accounts for the phenotypes since intragenic suppressors of tra1-L3733A restored Tra1 levels, and reducing wild-type Tra1 led to comparable growth defects. Also supporting a key role for the FATC domain in the structure/function of Tra1, addition of a C-terminal glycine residue resulted in decreased association with Spt7 and Esa1, and loss of cellular viability. These findings demonstrate the regulatory potential of mechanisms targeting the FATC domains of PIKK proteins

The Influence of Climate and Tectonics on the Geomorphology of the Western Slope of the Central Andes, Peru and Chile

This thesis explores the geomorphic evolution of the western Andean mountain front with respect to climate and tectonics for the area between 10?S and 33?S latitude. Much of the area I studied lies within the Atacama Desert, the most arid environment known on earth today. The development of a disequilibrium (or polyphase) landscape between 18?S and 22?S with the youngest phase of landscape development dominated by deep canyons suggests a progresson through time toward conditions favoring the development and preservation of groundwater sapping features. I interpret the shift to be related to uplift of the adjacent Altiplano Plateau, with consequent reduction in precipitation on the western Andean slope. In support of this, an estimated 1000 m of post-10 Ma uplift of the central Andes is determined by modeling the former downstream projections of knick-point bounded river segments in the rivers draining the area between 18? and 22?S (Northernmost Chile). The impact of climate on landforms is explored in detail by the relationships between mean annual precipitation (MAP), slopes measured from a 90 m DEM, and erosion rates. At the scale of the entire mountain front, there is a significant correlation between average slope at the hillslope scale and the modern climatology of the western Andean Mountain front between 10? and 33?S latitude. Detailed examination of the distribution of slopes at the hillslope scale for eight distinct mountain front regions reveal the consequences of allochthonous versus autochthonous mountain front moisture sources. At Approximately 100 mm/yr mean annual precipitation, slope distributions begin to reflect the dominance of fluvial landscapes. Reconstruction of a regionally extensive ~ 10 Ma depositional surface permitted the determination of erosional mass loss for the rivers that drain the western mountain front. Erosion rates were determined for 2 areas, on in a zone with a pronounced vertical precipitation gradient (18?S-22?S) and the other in an area with a strong latitudinal precipitation gradient (25?S-29.5?S). Landform data for the southern region show strong correlations between MAP, average slope and erosion rate. The northern area does not have strong correlations most likely due to the strong impact of allochthonous water sources.National Aeronautical and Space Administration Earth System Science Fellowship; National Science Foundation EAR-020813