Sample records for eopaleozoico precordillera mendocina

  1. Insights into catalytic action mechanism of Pseudomonas mendocina 3121-1 lipase

    Czech Academy of Sciences Publication Activity Database

    Bendikiene, V.; Surinenaite, B.; Juodka, B.; Šafaříková, Miroslava


    Roč. 34, - (2004), s. 572-577 ISSN 0141-0229 R&D Projects: GA AV ČR KSK4055109 Institutional research plan: CEZ:AV0Z6087904 Keywords : Pseudomonas mendocina * lipase Subject RIV: CE - Biochemistry Impact factor: 1.759, year: 2004

  2. The isolation and functional identification on producing cellulase of Pseudomonas mendocina (United States)

    Zhang, Jianfeng; Hou, Hongyan; Chen, Guang; Wang, Shusheng; Zhang, Jiejing


    ABSTRACT The straw can be degraded efficiently into humus by powerful enzymes from microorganisms, resulting in the accelerated circulation of N,P,K and other effective elements in ecological system. We isolated a strain through screening the straw degradation strains from natural humic straw in the low temperature area in northeast of china, which can produce cellulase efficiently. The strain was identified as Pseudomonas mendocina by using morphological, physiological, biochemical test, and molecular biological test, with the functional clarification on producing cellulase for Pseudomonas mendocina for the first time. The enzyme force constant Km and the maximum reaction rate (Vmax) of the strain were 0.3261 g/L and 0.1525 mg/(min.L) through the enzyme activity detection, and the molecular weight of the enzyme produced by the strain were 42.4 kD and 20.4 kD based on SDS-PAGE. The effects of various ecological factors such as temperature, pH and nematodes on the enzyme produced by the strain in the micro ecosystem in plant roots were evaluated. The result showed that the optimum temperature was 28°C, and the best pH was 7.4∼7.8, the impact heavy metal was Pb2+ and the enzyme activity and biomass of Pseudomonas mendocina increased the movement and predation of nematodes. PMID:27710430

  3. High-resolution stable isotope stratigraphy of the upper Cambrian and Ordovician in the Argentine Precordillera

    DEFF Research Database (Denmark)

    Sial, A.N.; Peralta, S.; Gaucher, C.


    We report the occurrence of important carbon isotope excursions in early Paleozoic formations of the Eastern and Central Argentine Precordillera. The Steptoean positive isotope carbon excursion (SPICE) is known from North America, Kazakhstan, South China, Australia and South America, and the nega......We report the occurrence of important carbon isotope excursions in early Paleozoic formations of the Eastern and Central Argentine Precordillera. The Steptoean positive isotope carbon excursion (SPICE) is known from North America, Kazakhstan, South China, Australia and South America......, and the negative isotope carbon excursion (SNICE) has been described for the first time in South America. We report here the record of the SPICE and SNICE in a single section in the Eastern Precordillera. In the Central Precordillera, a minor middle Darriwilian positive carbon isotope excursion (MDICE) and a late...

  4. Faulting and erosion in the Argentine Precordillera during changes in subduction regime: Reconciling bedrock cooling and detrital records (United States)

    Fosdick, Julie C.; Carrapa, Barbara; Ortíz, Gustavo


    The Argentine Precordillera is an archetypal retroarc fold-and-thrust belt that records tectonics associated with changing subduction regimes. The interactions between exhumation and faulting in the Precordillera were investigated using apatite and zircon (U-Th-Sm)/He and apatite fission track thermochronometry from the Precordillera and adjacent geologic domains. Inverse modeling of thermal histories constrains eastward in-sequence rock cooling associated with deformation and erosion from 18 to 2 Ma across the Central Precordillera tracking thrusting during this time. The youngest AHe ages (5-2 Ma) and highest erosion rates are located in the eastern and western extremities of the Precordillera and indicate that recent denudation is concentrated at its structural boundaries. Moreover, synchronous rapid Pliocene cooling of the Frontal Cordillera, Eastern Precordillera, and Sierra del Valle Fértil was coeval with initiation of basement-involved faulting in the foreland. Detrital zircon U-Pb geochronology from the ca. 16-8.1 Ma Bermejo foreland basin strata suggests fluvial connectivity westward beyond the Frontal Cordillera to the Main Cordillera and Coast Range followed by an important shift in sediment provenance at ca. 10 Ma. At this time, we suggest that a substantial decrease in Permo-Triassic igneous sources in the Frontal Cordillera and concurrent increase in recycled zircons signatures of Paleozoic strata are best explained by uplift and erosion of the Precordillera during widening of the thrust-belt. Bedrock thermochronology and modeling indicate a 2-6 Myr lag time between faulting-related cooling in the hinterland and the detrital record of deformation in the foreland basin, suggesting that for tectonically active semi-arid settings, bedrock cooling may be more sensitive to onset of faulting. We suggest that high erosion rates in the Frontal Cordillera and Eastern Precordillera are associated with increased interplate coupling during shallowing of the

  5. Clasificación de yeso mediante imágenes ASTER en la Cordillera Principal Mendocina


    José F Mescua


    Se presenta una metodología para obtener el mapa de distribución de yeso con imágenes satelitales ASTER. Se utilizaron imágenes con nivel de procesamiento ASTERL3A correspondientes a dos áreas de la Cordillera Principal mendocina. La estratigrafía de las áreas de estudio se encuentra compuesta por una espesa sucesión sedimentaria mesozoica, volcanitas cenozoicas y depósitos cuaternarios. Dentro de los depósitos mesozoicos se encuentra la Formación Auquilco, integrada por yeso y anhidrita. El ...

  6. Replegamiento de láminas de corrimiento epidérmicas mediante fallas inversas de basamento activas en la Precordillera Oriental del oeste de Argentina


    Meigs, A.; Krugh, W. C.; Schiffman, C.; Vergés, Jaume; Ramos, V. A.


    Devastating earthquakes like the 1944 San Juan earthquake reflect active deformation in western Argentina. Although the earthquake caused considerable damage to San Juan, the source of the earthquake remains uncertain. Potential source faults occur in the thin-skinned fold-and-thrust belt Precordillera province and in the thick-skinned Sierras Pampeanas province, to the west and east, respectively of Sierra de Villicum, a thrust sheet in the eastern Precordillera northwest of San Juan. Sierra...

  7. Lower and Middle Devonian Malvinokaffric ostracods from the Precordillera Basin of San Juan, Argentina (United States)

    Salas, María J.; Rustán, Juan J.; Sterren, Andrea F.


    Ostracod from the upper Lower to Middle Devonian rocks of the Argentine Precordillera Basin (Talacasto and Punta Negra formations) are studied. One new genus Pircawayra nov. gen., and five species (including three new: Pircawayra gigantea nov. gen. and sp., Lapazites trinodis nov. sp. and Keslingiella? teresae nov. sp.) are defined. The recorded ostracod fauna closely resembles that coeval from Bolivia and South Africa, exhibiting a remarkable endemism, not only at the genus level, but also at the species level. In addition to its low-diversity, the Malvinokaffric ostracod association is also characterized by having large, thick, coarsely ornamented and swollen valves. The similar ostracod composition from the Andean and South African basins suggests faunal exchange between these two areas. Based on the ostracod faunas, the Malvinokaffric Realm is clearly recognizable at least up to the Middle Devonian.

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

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


    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

  9. Ordovidan K-bentonites in the Precordillera of San Juan and its tectomasmatic significance (United States)

    Cingolani, C.A.; Huff, W.; Bergstrom, S.; Kolata, D.


    A succession of approximately 35 early Middle Ordovician K-bentonite beds are exposed in the Precordillera region near the town of Jachal, in San Juan Province (at Cerro Viejo and La Chilca sections). They occur in argillaceous limestone in the upper part of the San Juan Limestone and in the interbedded shales and mudstones at the base of the overlying Los Azules Formation. Total thickness of the K-bentonite-bearing interval is 23 m and individual beds range from 1 to 65 cm thick. An essentially Arenig-Llanvirn age for the K-bentonite succession is indicated by the presence of graptolites diagnostic of the Paraglossograptus tentaculatus Zone and conodonts indicating the Eoplacognathus suecicus Zone. The bentonites consist mainly of Rl ordered illite/smectite, characteristic of most of the lower Paleozoic K-bentonites, plus volcanogenic crystals. Similar to other K-bentonites, these probably represent the distal, glass-rich portion of fall-out ash beds derived from collision zone explosive volcanism. The geochemical data and preliminary plots on the magmatic discrimination diagram indicate the parental magma was of rhyolite to trachyandesite composition. Tectonic discrimination diagrams show the setting of Cerro Viejo ash layers as falling on the boundary between volcanic arc and within plate rocks, typical of collision margin felsic volcanic rocks. U-Pb isotope dating for two zircon fractions from one sample show a lower concordia intercept of 461, +7-10 Ma coincident with the biostratigraphic age. Thus, they have important implications for the origin and early history of the allochtonous Precordillera terrane and the Pacific margin of South America. Furthermore, they are potentially important in interpretations of the paleogeographic relations of Laurentia and Gondwana during Ordovician time. ?? 1997 Asociacio??n Geolo??gica Argentina.

  10. Growth stratal records of instantaneous and progressive limb rotation in the Precordillera thrust belt and Bermejo basin, Argentina (United States)

    Zapata, TomáS. R.; Allmendinger, Richard W.


    Analysis of synorogenic deposits preserved near the thrust front zone of the Precordillera fold and thrust belt and in the Bermejo foreland basin in central Argentina documents the evolution of deformation during the last 5 Myr as well as the thrust system kinematics. Seismic lines across the area display examples of progressive and instantaneous limb rotations. The easternmost thrust plate of the Central Precordillera, the Niquivil thrust, experienced episodic motion in two main stages: a first thrust movement as a fault-propagation fold and a second movement as a high-angle anticlinal breakthrough fault after a period of quiescence. Growth strata deposited in the La Pareja intermontane basin and the Las Salinas and Bermejo anticline recorded continuous growth of Eastern Precordilleran structures beginning at ˜2.7 Ma, with uplift rates of ˜0.3 mm/yr for the Niquivil anticline, 1.08 mm/yr for the Las Salinas anticline, and between ˜0.6 and 0.38 mm/yr during the last ˜2 Myr for the Bermejo anticline. Once the Eastern Precordillera began to grow, the propagation of the Niquivil thrust stopped, restricting the deformation to the young Vallecito out-of sequence thrust. The complex geometry of growth strata deposited on the back limb of the Las Salinas anticline can be explained by using a model of a two-step fault propagation fold with constant layer thickness. The Bermejo anticline of the Eastern Precordillera is formed by the simultaneous propagation of a shallow fault, responsible for the fold shape, and a deep fault that produced vertical uplift. A growth triangle that documents instantaneous forelimb rotation for a fault-propagation fold is recorded for the first time in a published seismic line.

  11. Cenozoic sedimentation and exhumation of the foreland basin system preserved in the Precordillera thrust belt (31-32°S), southern central Andes, Argentina (United States)

    Levina, Mariya; Horton, Brian K.; Fuentes, Facundo; Stockli, Daniel F.


    Andean retroarc compression associated with subduction and shallowing of the oceanic Nazca plate resulted in thin-skinned thrusting that partitioned and uplifted Cenozoic foreland basin fill in the Precordillera of west-central Argentina. Evolution of the central segment of the Precordillera fold-thrust belt is informed by new analyses of clastic nonmarine deposits now preserved in three intermontane regions between major east directed thrust faults. We focus on uppermost Oligocene-Miocene basin fill in the axial to frontal Precordillera at 31-32°S along the Río San Juan (Albarracín and Pachaco sections) and the flank of one of the leading thrust structures (Talacasto section). The three successions record hinterland construction of the Frontal Cordillera, regional arc volcanism, and initial exhumation of Precordillera thrust sheets. Provenance changes recorded by detrital zircon U-Pb age populations suggest that initial shortening in the Frontal Cordillera coincided with an early Miocene shift from eolian to fluvial accumulation in the adjacent foreland basin. Upward coarsening of fluvial deposits and increased proportions of Paleozoic clasts reflect cratonward (eastward) advance of deformation into the Precordillera and resultant structural fragmentation of the foreland basin into isolated intermontane segments. Apatite (U-Th)/He thermochronometry of basin fill constrains to 12-9 Ma the most probable age of uplift-induced exhumation and cooling of Precordillera thrust sheets. This apparent pulse of exhumation is evident in each succession, suggestive of rapid, large-scale exhumation by synchronous thrusting above a single décollement linking major structures of the Precordillera.

  12. Development of a real-time TaqMan assay to detect mendocina sublineage Pseudomonas species in contaminated metalworking fluids. (United States)

    Saha, Ratul; Donofrio, Robert S; Bagley, Susan T


    A TaqMan quantitative real-time polymerase chain reaction (qPCR) assay was developed for the detection and enumeration of three Pseudomonas species belonging to the mendocina sublineage (P. oleovorans, P. pseudoalcaligenes, and P. oleovorans subsp. lubricantis) found in contaminated metalworking fluids (MWFs). These microbes are the primary colonizers and serve as indicator organisms of biodegradation of used MWFs. Molecular techniques such as qPCR are preferred for the detection of these microbes since they grow poorly on typical growth media such as R2A agar and Pseudomonas isolation agar (PIA). Traditional culturing techniques not only underestimate the actual distribution of these bacteria but are also time-consuming. The primer-probe pair developed from gyrase B (gyrB) sequences of the targeted bacteria was highly sensitive and specific for the three species. qPCR was performed with both whole cell and genomic DNA to confirm the specificity and sensitivity of the assay. The sensitivity of the assay was 10(1) colony forming units (CFU)/ml for whole cell and 13.7 fg with genomic DNA. The primer-probe pair was successful in determining concentrations from used MWF samples, indicating levels between 2.9 x 10(3) and 3.9 x 10(6) CFU/ml. In contrast, the total count of Pseudomonas sp. recovered on PIA was in the range of <1.0 x 10(1) to 1.4 x 10(5) CFU/ml for the same samples. Based on these results from the qPCR assay, the designed TaqMan primer-probe pair can be efficiently used for rapid (within 2 h) determination of the distribution of these species of Pseudomonas in contaminated MWFs.

  13. Crustal structure of the Central Precordillera of San Juan, Argentina (31°S) using teleseismic receiver functions (United States)

    Ammirati, Jean-Baptiste; Alvarado, Patricia; Perarnau, Marcelo; Saez, Mauro; Monsalvo, Guillermo


    The subduction of the Nazca plate under the South American plate around 31°S is characterized by flat slab geometry. The (Chilean) Pampean flat slab of Argentina associated with the subduction of the Juan Fernandez ridge lies in a region of a series of foreland uplifts corresponding to the thin-skinned Precordillera and basement cored Sierras Pampeanas ranges. The SIEMBRA project deployed 40 broadband stations in 2008-2009 in both the Precordillera and the Sierras Pampeanas with the aim to foster the understanding of the entire central Andean flat slab region. One of the SIEMBRA station (DOCA) located on the western flank of Sierra de la Invernada in the Central Precordillera appears particularly appropriate to study the crustal structure and eventually detect discontinuities related to terranes establishment. We thus performed a receiver function analysis using teleseismic data recorded at the DOCA station during the SIEMBRA project and from October 2011 to June 2012 using a broadband UNSJ (National University of San Juan) seismic station with the purpose to obtain crustal images with details of the intracrustal structure consistent with a mechanism that could explains both the observed earthquake depths and the uplift pattern in the Central Precordillera. Our results show that the Moho beneath the Precordillera lies at a depth of about 66 km. The Moho signal appears diminished and behaves irregularly as a function of azimuthal orientations. Although this observation could be the result of an irregular geometry it also correlates with the hypothesis of partial eclogitisation in the lower crust. Two mid-crustal discontinuities have also been revealed. The shallower one could correspond to a décollement level between the Precordilleran strata and the Cuyania basement at 21 km depth. The deeper one which the presence has been matched with a sharp decrease of the crustal seismic activity drove us to the hypothesis of a major change in crustal composition at 36 km

  14. Differential effects of Pseudomonas mendocina and Glomus intraradices on lettuce plants physiological response and aquaporin PIP2 gene expression under elevated atmospheric CO2 and drought. (United States)

    Alguacil, Maria Del Mar; Kohler, Josef; Caravaca, Fuensanta; Roldán, Antonio


    Arbuscular mycorrhizal (AM) symbiosis and plant-growth-promoting rhizobacterium (PGPR) can alleviate the effects of water stress in plants, but it is unknown whether these benefits can be maintained at elevated CO2. Therefore, we carried out a study where seedlings of Lactuca sativa were inoculated with the AM fungus (AMF) Glomus intraradices N.C. Schenk & G.S. Sm. or the PGPR Pseudomonas mendocina Palleroni and subjected to two levels of watering and two levels of atmospheric CO2 to ascertain their effects on plant physiological parameters and gene expression of one PIP aquaporin in roots. The inoculation with PGPR produced the greatest growth in lettuce plants under all assayed treatments as well as the highest foliar potassium concentration and leaf relative water content under elevated [CO2] and drought. However, under such conditions, the PIP2 gene expression remained almost unchanged. G. intraradices increased significantly the AMF colonization, foliar phosphorus concentration and leaf relative water content in plants grown under drought and elevated [CO2]. Under drought and elevated [CO2], the plants inoculated with G. intraradices showed enhanced expression of the PIP2 gene as compared to P. mendocina or control plants. Our results suggest that both microbial inoculation treatments could help to alleviate drought at elevated [CO2]. However, the PIP2 gene expression was increased only by the AMF but not by the PGPR under these conditions.

  15. Late Cenozoic basin evolution and fold-thrust deformation in the southern Central Andes: Initial constraints from synorogenic deposits of the Precordillera, Argentina (United States)

    Levina, M.; Horton, B. K.; Fuentes, F.; Stockli, D. F.


    In the Precordillera region of the Argentine Andes, Cenozoic shortening associated with flattening of the Pampean segment of the subducting Nazca plate has resulted in a series of thin skinned fold-thrust systems that partitioned and uplifted Cenozoic foreland basin deposits. The kinematic and temporal evolution of the Andean Precordillera can be approached through detailed analyses of the sedimentary fill now preserved in intermontane regions and the bedrock low-temperature thermochronology of the fold-thrust belt. In this project, we focus on Neogene foreland basin fill exposed in the central and eastern Precordillera along the San Juan River (Quebrada Albarracín and Pachaco regions), on the western flank of the Sierra Talacasto, and in the Loma de las Tapias area near the Ullum dam. The sedimentary successions exposed in these regions record the hinterland development of the Frontal Cordillera (detrital zircon provenance and composition of sandstone and conglomeratic units), regional volcanism (pyroclastic flows and tuffaceous sandstone units), and initial construction of the Precordillera (fault cutoff relationships, growth strata, and paleocurrent changes). We investigate the development and subsequent partitioning and deformation of these synorogenic sections using sediment provenance (detrital zircon U-Pb geochronology, conglomerate clast counts, sandstone petrography, and paleocurrent measurements), facies analysis of measured stratigraphic successions, and initial apatite (U-Th)/He cooling histories to constrain the age of uplift-induced exhumation of successive thrust sheets in the Andean Precordillera.

  16. Multiple geophysical methods examining neotectonic blind structures in the Maradona valley, Central Precordillera (Argentina) (United States)

    Lara, Gabriela; Klinger, Federico Lince; Perucca, Laura; Rojo, Guillermo; Vargas, Nicolás; Leiva, Flavia


    A high-resolution superficial geophysical study was carried out in an area of the retroarc region of the Andes mountains, located in the southwest of San Juan Province (31°45‧ S, 68°50‧ W), Central Precordillera of Argentina. The main objectives of this study were to confirm the presence of blind neotectonic structures and characterize them by observing variations in magnetic susceptibility, density and p-wave velocities. Geological evidence demonstrates the existence of a neotectonic fault scarps affecting Quaternary alluvial deposits in eastern piedmont of de Las Osamentas range, in addition to direct observation of the cinematic of this feature in several natural exposures. The Maradona valley is characterized by the imbricated eastern-vergence Maradona Fault System that uplifts Neogene sedimentary rocks (Albarracín Formation) over Quaternary (Late Pleistocene-Holocene) alluvial deposits. The combined application of different geophysical methods has allowed the characterization of a blind fault geometry also identified on a natural exposure. The magnetic data added to the gravimetric model, and its integration with a seismic profile clearly shows the existence of an anomalous zone, interpreted as uplifted blocks of Miocene sedimentary rocks of Formation Albarracín displaced over Quaternary deposits. The application and development of different geophysical methods, together with geological studies allow to significantly improving the knowledge of an area affected by Quaternary tectonic activity. Finally, this multidisciplinary study, applied in active blind structures is very relevant for future seismic hazard analysis on areas located very close to populated centers.

  17. Fault-related carbonate breccia dykes in the La Chilca area, Eastern Precordillera, San Juan, Argentina (United States)

    Castro de Machuca, Brígida; Perucca, Laura P.


    Carbonate fault breccia dykes in the Cerro La Chilca area, Eastern Precordillera, west-central Argentina, provide clues on the probable mechanism of both fault movement and dyke injection. Breccia dykes intrude Upper Carboniferous sedimentary rocks and Triassic La Flecha Trachyte Formation. The timing of breccia dyke emplacement is constrained by cross cutting relationships with the uppermost Triassic unit and conformable contacts with the Early Miocene sedimentary rocks. This study supports a tectonic-hydrothermal origin for these breccia dykes; fragmentation and subsequent hydraulic injection of fluidized breccia are the more important processes in the breccia dyke development. Brecciation can be triggered by seismic activity which acts as a catalyst. The escape of fluidized material can be attributed to hydrostatic pressure and the direction of movement of the material establishes the direction of least pressure. Previous studies have shown that cross-strike structures have had an important role in the evolution of this Andean segment since at least Triassic times. These structures represent pre-existing crustal fabrics that could have controlled the emplacement of the dykes. The dykes, which are composed mostly of carbonate fault breccia, were injected upward along WNW fractures.

  18. Geological interpretation of Landsat TM imagery and aeromagnetic survey data, northern Precordillera region, Argentina (United States)

    Chernicoff, C. J.; Nash, C. R.


    This case study demonstrates a methodology for obtaining maximum geoscientific value from reconnaissance (1000 m line spacing) aeromagnetic data through integration with high-resolution satellite imagery. In this study, lithostratigraphic interpretation of optimally processed Landsat TM data at reconnaissance mapping scale (1:100,000) has been carried out as a precursor to geophysical interpretation, providing the basic 'framework' in which to view the imaged geophysical data. The Landsat-derived framework shows the correct positions and vergences of major structures, which characterize this part of the Andean foreland thrust-and-fold belt. Within the structural framework derived from satellite imagery, the locations of major shallow-source aeromagnetic anomalies related to intermediate/mafic extrusive and subvolcanic rocks and the controlling structures of these economically important magmatic events can be correctly interpreted. Results of the study indicate a significant, coherent, and previously unrecognized post-Permian, pre-Miocene volcanic/subvolcanic center, which is probably associated with regional sinistral strike-slip along a reactivated N-S accretionary suture and a pre-existing Precambrian/Paleozoic basement structure. Subsequent west-vergent thick-skinned thrusting associated with uplift of Sierra Valle Fertil Precambrian block has developed a set of distinctive NW-oriented strike-slip faults at the site of the volcanic center. The NW structures cut and rotate late Miocene thin-skinned structures associated with the Precordillera fold-and-thrust belt. Intrusive rocks associated with the inferred Oligocene volcanic center form easily recognizable, partially remanent dipole anomalies, are associated with alteration and Au mineralization (Cerro Guachi, El Pescado, Gnrl. Belgrano mines), and are located along NW-oriented sinistral splay faults. The strike-slip related tectonic/magmatic event is currently regarded as Oligocene in age and may correlate

  19. Timing and nature of alluvial fan and strath terrace formation in the Eastern Precordillera of Argentina (United States)

    Hedrick, Kathryn; Owen, Lewis A.; Rockwell, Thomas K.; Meigs, Andrew; Costa, Carlos; Caffee, Marc W.; Masana, Eulalia; Ahumada, Emilio


    Sixty-eight 10Be terrestrial cosmogenic nuclide (TCN) surface exposure ages are presented to define the timing of alluvial fan and strath terrace formation in the hyper-arid San Juan region of the Argentine Precordillera. This region is tectonically active, and numerous fault scarps traverse Quaternary landforms. The three study sites, Marquesado strath complex, Loma Negra alluvial fan and Carpintería strath complex reveal a history of alluvial fan and strath terrace development over the past ˜225 ka. The Marquesado complex Q3m surface dates to ˜17 ± 3 ka, whereas the Loma Negra Q1ln, Q2ln, Q3ln, Q4ln, and Q5ln surfaces date to ˜24 ± 3 ka, ˜48 ± 2 ka, ˜65 ± 13 ka, ˜105 ± 21 ka, and ˜181 ± 29 ka, respectively. The Carpintería complex comprises eight surfaces that have been dated and include the Q1c (˜23 ± 3 ka), Q2c (˜5 ± 5 ka), Q3ac (˜25 ± 12 ka), Q3bc (˜29 ± 15 ka), Q4c (˜61 ± 12 ka), Q5c (˜98 ± 18 ka), Q6c (˜93 ± 18 ka), and Q7c (˜212 ± 37 ka). 10Be TCN depth profile data for the Loma Negra alluvial fan complex and Carpintería strath terrace complex, as well as OSL ages on some Carpintería deposits, aid in refining surface ages for comparison with local and global climate proxies, and additionally offer insights into inheritance and erosion rate values for TCNs (˜10 × 10410Be atoms/g of SiO2 and ˜5 m Ma-1, respectively). Comparison with other alluvial fan studies in the region show that less dynamic and older preserved surfaces occur in the Carpintería and Loma Negra areas with only younger alluvial fan surfaces preserved both to the north and south. These data in combination with that of other studies illustrate broad regional agreement between alluvial fan and strath terrace ages, which suggests that climate is the dominant forcing agent in the timing of terrace formation in this region.

  20. Paleogeographic significance of Clavohamulus hintzei Miller (Conodonta) and other Ibexian conodonts in an early Paleozoic carbonate platform facies of the Argentine Precordillera (United States)

    Lehnert, O.; Miller, J.F.; Repetski, J.E.


    Pre-Tremadocian conodonts and trilobites and Tremadocian conodonts are reported from the Cambrian and Ordovician La Silla Formation in the Cerro La Silla section in east-southeast Ja??chal, San Juan Province, Argentina. A shallow marine conodont fauna contains elements of Clavohamulus hintzei Miller, a common species in North America, but reported for the first time from the early Paleozoic platform carbonates of the western Argentine Precordillera. The presence of this species suggests a correlation with the Clavohamulus hintzei conodont subbiozone of the Cordylodus intermedius conodont biozone in North America, considered Early Ordovician (Skullrockian Stage, Ibexian Series) in North America, but by South American and European standards, this biozone would be of latest Cambrian age. C. hintzei and associated conodonts of the La Silla Formation are typical of the tropical faunas of the North American Midcontinent Faunal Province; Late Cambrian trilobites from lower in the formation also are typical North American taxa. The presence of these faunas in the platform carbonates is consistent with plate reconstructions suggesting that the Precordillera was in a tropical or subtropical position close to Laurentia during the late Precambrian and early Paleozoic. These new paleontological data provide one more argument for recent models of the Precordillera as a displaced terrane derived from the Ouachita Embayment at the southern margin of Laurentia.

  1. New data on neotectonic contractional structures in Precordillera, south of Río de La Flecha: Structural setting from gravity and magnetic data. San Juan, Argentina (United States)

    Perucca, Laura P.; Ruiz, Francisco


    The Central and Eastern Precordillera form oppositely verging thrust systems on the western and eastern sides of the Matagusanos-Maradona-Acequión valley, establishing a thick-skinned triangle zone with significant changes in the axis position along strike. Between the del Agua and the de La Fecha rivers, the axis of this triangular zone is located in the eastern portion of the depression. Changes in the position of the triangle zone axis along strike, whether to the east or to the west, took place during Pliocene-Pleistocene times. Geophysical and geodetic data indicate a subsurface structure striking NE, oblique to the general direction of the foreland with dextral displacement. Accordingly, the change in the location of the triangular area could be attributed to stress transfer controlled by heterogeneities in the basement. By analytic signal analysis of magnetic anomalies, it is possible to assess the regional structural coupling between Pie de Palo and Eastern Precordillera. The oblique arrangement of basement blocks could explain transverse lineaments and the sigmoidal geometry of the Eastern Precordillera. Geophysical and geological evidence shows that the depression is crossed by several E-W strike-slip faults. These faults possibly controlled the position of the triangle zone axis until Neogene-Pleistocene times by transferring displacements and provoking its jump along strike.

  2. New fission-track ages of mio-pliocene tuffs in the Sierras Pampeanas and Precordillera of Argentina

    International Nuclear Information System (INIS)

    Tabbutt, K.; Naeser, C.W.; Jordan, T.E.; Cerveny, P.F.


    Fission-track dates were determined for 18 volcanic tuff horizons located in nine Neogene foreland basin sequences distributed throughout the Precordillera and Sierras Pampeanas of Northwestern Argentina, an area of nearly horizontal subduction. These and other data indicate that a lower age limit for the sedimentary sequences studied is approximately 17 Ma. Therefore these fission-track dates constrain both the history of volcanic activity and the time of deposition in several foreland basins from the middle Miocene to Recent. Although the dates range from 3.6±0.8 Ma to 17.0±1.9 Ma, there is a marked increase in the number of ashes younger than 9 Ma. This implies that two distinct episodes of volcanic activity affected the region. The source of some of these tuffs is unknown but they are probably limited to the 'flat-slab' region between 27 deg and 32 deg S. Tuffs at Rio Blanco and Santa Florentina that are spatially associated with the Mogotes dacite domes of the Famatina Range represented magmatism bracketed from about 7 to 4 Ma in the region underlain by the flat-subducted plate. The stratigraphic relations in the basins show that the faulting that uplifted Sierra de Famatina was contemporaneous with the volcanism which reached the surface along the bounding faults. (Author) [es

  3. Sedimentology of middle ordovician carbonates in the Argentine precordillera: evidence of regional relative sea-level changes (United States)

    Keller, M.; Eberlein, S.; Lehnert, O.


    The Las Aguaditas Formation in the Argentine Precordillera of San Juan is the only Ordovician carbonate sequence deposited on a slope. Spiculites, mudstones and calcisiltites represent the autochthonous sediments, characterized by a fine lamination, rare fossils and their dark colour. The pelagic fauna consists of rare radiolarians/calcispheres, trinucleid trilobites, graptolites and conodonts. The latter are typical of an open marine environment and proved a Llanvirn—Llandeilo age for the Las Aguaditas Formation. In the upper part of the succession there are several intercalations of megabreccias. Their thickness decreases from about 20 to 4 m towards the top of the formation, accompanied by an increasing amount of carbonate turbidites. The clasts of the breccias are derived from the slope as well as the platform. Each of the megabreccia horizons represents a system of channels, lobes and interchannel deposits, which together form a slope apron. On top of the lower breccia a small biostrome developed, where bryozoans and crinoids are preserved in an autochthonous position. Sedimentation of the Las Aguaditas Formation started with the drowning of the underlying carbonate platform (San Juan limestones). Near the Arenig-Llanvirn boundary, a rapid ecstatic sea-level rise led to the deposition of graptolitic black shales and mudstones. Upwards, allochthonous carbonates become increasingly abundant. The onset of megabreccia deposition coincides with a major relative sea-level fall, caused by block movements in connection with rifting. The subsequent transition from breccia formation towards turbiditic sedimentation corresponds to an environmental shift from the slope towards the toe of slope and basin and marks a renewed moderate sea-level rise.

  4. Within plate seismicity analysis in the segment between the high Cordillera and the Precordillera of northern Mendoza (Southern Central Andes

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    Julián Olivar


    Full Text Available Crustal seismicity in northwestern Mendoza Province in Argentina, corresponding to the transition zone between the Chilean-Pampean flat subduction zone (26.5–33.5°S and the Southern Central Andes normal subduction zone to the south, is studied in order to i identify its relationship with the mapped structure, ii determine deformational mechanisms and iii constrain the geometry of the fold and thrust belt in the lower crust. Through this, we aim to determine which are the structures that contribute to Andean construction, east of the Frontal Cordillera in Argentina and at the western Principal Cordillera in Chile. Data from a temporary local seismic network are reprocessed in order to achieve a precise location of hypocenters and, whenever possible, to build focal mechanisms. Results are interpreted and compared with previous seismic studies and structural models. Analyzed seismicity is grouped around the eastern front of Frontal Cordillera, with hypocenters mainly at depths of 25–40 km. Contrastingly, earthquakes in the Principal Cordillera to the west are located at the axial Andean sector and Chilean slope, with depths shallower than 15 km. Obtained focal mechanisms indicate mainly strike-slip displacements, left lateral at Frontal Cordillera and right lateral at Principal Cordillera. Based on these observations, new possible structural models are proposed, where seismogenic sources could be either associated with inherited basement structures from the Cuyania-Chilenia suture; or correspond to deep-blind thrusts linked with a deeper-than-previously-assumed decollement that could be shared between Frontal Cordillera and western Precordillera. This deeper decollement would coincide in turn with the one determined from receiver function analysis for the eastern Sierras Pampeanas in previous works, potentially implying a common decollement all through the fold and thrust belt configuration. Apart from this, a new interpretation of

  5. Late Quaternary evolution of the La Cantera Fault System (Central Precordillera, Argentina): A morphotectonic and paleoseismic analysis (United States)

    Perucca, Laura; Rothis, Martín; Bezerra, Francisco Hilario; Vargas, Nicolás; Lima, Jean


    The La Cantera Fault System (LCFS) is the most active Quaternary structure in the Central Precordillera of San Juan, in central-western Argentina; the system extends for 47 km along the intermountain valley that separates the Sierra de La Cantera and La Invernada, north of the San Juan River. The average fault trend is 20°; it dips at angles varying between 15° and 30° W in the northern section, to approximately 40° W in the central section, and up to 60° W in the southern section. The fault affects Holocene to recent alluvium deposits in the western piedmont of the Sierra de La Cantera and is defined by a series of landforms found in compressive tectonic environments, including simple and compound counterslope fault scarps, staircased alluvial terraces, sag ponds, flexural scarps, aligned springs, broom-shaped drainage patterns, river diversions, beheaded channels, changes in incision depths, sinuosity and a river gradient along channels. Trench investigations indicated that at least three events occurred in the past 1.1-10.1 ky. The topographic profiles of the selected channels and interfluves cutting across the northern and central trace of the fault were analyzed using a Stonex Vector GPS differential system to establish the relationship between the topography and slope of the rivers. This morphometric analysis of scarps indicates that active tectonics have played an essential role in controlling the drainage pattern in the piedmont, leading the rivers to adjust to these slope variations. Based on the analyzed geomorphologic, stratigraphic and structural characteristics, the LCFS is considered to be a relevant seismogenic source in the intraplate portion of southern South America, with a recurrence interval of at least 2000 ± 500 years for moderate magnitude earthquakes during the last 11,000 years.

  6. Tectofacies ordovícicas y evolución de la cuenca eopaleozoica de la precordillera Argentina

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    Astini, R. A.


    Full Text Available After a typical passive margin setting during the Cambrian, two basically different tectofacies evolved simultaneously and mostly independently during the Ordovician in the Argentinean Precordillera basin. The eastern domain characterizes epicontinental depositional systems developed on a stable margin, while the western domain is composed of deep-sea turbiditic systems which developed on a high subsidence «cuasioceanic» substratum. The two domains were set aside during the Ocloyic movements and later tectonic phases of the Caledonic cycle. A regional unconformity developed by upwarping of the former platform (eastern domain conforms the downlaping surface of the Late Ordovician and Silurian siliciclastic shallow marine sequences. This regional doming is interpreted as a peripheral bulge in an incipient foreland basin caused by a type A subduction to the present west. This hypothesis is quite different from former ones and solves most of the stratigraphic and architectural problems during the Ordovician and Silurian Silurian and Devonian depocenters are mainly localized on the eastern domain and conform a succession of shallow marine sequences, which commonly characterize forelands. The different unconformities affecting the Silurian and Devonian deposits are interpreted as basin relaxation periods and as global sea-level oscillations. The Late Devonian Chanic diastrophysm involved an important shortening (definitive annexation of the two domains and caused the main paleogeographic rearrangement, supported by the regional angular unconformity which separates the Lower Palaeozoic from the Upper Palaeozoic continental deposits.Desde un punto de vista regional, el Sistema Ordovícico de la Precordillera del centrooeste argentino puede subdividirse en dos tectofacies que habrían evolucionado paralelamente y en contextos casi independientes una de otra, acreccionadas durante la Orogenia Oclóyica y fases posteriores del Ciclo Caledónico. La

  7. Taxonomía y biogeografía de cuatro especies de Psectrascelis (Coleoptera: Tenebrionidae de la Precordillera y Cordillera de los Andes en Mendoza, Argentina

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    Gustavo E. FLORES


    Full Text Available El género neotropical Psectrascelis Solier (Pimeliinae: Nycteliini comprende 75 especies que se distribuyen desde el sur de Perú hasta el sur de Argentina y Chile. En este aporte se revisan las cuatro especies de Psectrascelis que habitan en el noroeste de la provincia de Mendoza (Argentina, en los cordones montañosos de la Precordillera y Cordillera de los Andes: P. deplanata (Lacordaire, 1830, P. vestita (Lacordaire, 1830, P. mamillonea (Lacordaire, 1830 y P. semistrigosa Fairmaire, 1903. Se proveen redescripciones con nuevos caracteres morfológicos, fotografías de adultos y de los pronotos, e ilustraciones de genitalia masculinos. Se consigna la distribución geográfica y rangos altitudinales para cada especie, estableciendo las provincias biogeográficas que habitan. Se presenta una discusión acerca de los patrones de distribución de las especies de Psectrascelis y de otros artrópodos epigeos que habitan en los cordones montañosos de la Precordillera y Cordillera de los Andes.

  8. Analysis of neotectonic structures in the Eastern Precordillera of Argentina in relation to seismic hazard by the application of integrated geophysical methods (United States)

    Correa-Otto, Sebastián; Ariza, Juan; Lince Klinger, Federico; Giménez, Mario; López Hidalgo, Andrés


    The city of San Juan, in the Central-Western region of Argentina, has been the target of very destructive superficial earthquakes, some of which have not been associated to a clear structural source up to this date. The city is constantly growing outside the valley where it is located, towards the area of Eastern Precordillera which is currently having an increased socio-cultural activity. Thus, this study is focused on increasing the geological knowledge of the latter by studying the eastern flank of Sierra Chica de Zonda (Eastern Precordillera) whose proved neotectonic activity represents a geohazard. On the basis of the general geological setting the neotectonic structures in the study area are related to a major active synclinal folding located just under the western sector of the San Juan city. Geophysical potential methods (gravimetric and magnetometric surveys) were used to recognize contacts by contrast of density and magnetic susceptibility. In order to reduce the ambiguity of these methods the gravi-magnetometric results were constrained by using seismic and electrical tomographies. These contacts where geophysical properties abruptly change, were interpreted as faults despite many of them not having a superficial expression. The latter being of great importance to asses the seismic hazard of the study area.

  9. Tradición y reacción en el Sesquicentenario: La escuela sevillana mendocina Tradition and reaction in the sesquicentennial: The Sevillian school of Mendoza

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    María Celina Fares


    Full Text Available La indagación sobre el nacionalismo en el posperonismo en Mendoza nos ha permitido recuperar una serie de itinerarios intelectuales que dan cuenta de la complejidad de un período, en el que la circulación y tránsito de ideas evidencian no sólo fuertes procesos de mutación de identidades, sino también la cristalización de posiciones ciertamente anacrónicas. En este trabajo pretendemos relevar a propósito de la celebración del sesquicentenario de Mayo la producción historiográfica mendocina que circuló en espacios de divulgación, constituyéndose en una fuerte tradición que perduró en los espacios académicos locales. Más allá de explicar la incidencia que tuvieron en la refracción de otras corrientes de pensamiento, las tesis interpretativas que ven a Mayo como un momento de reafirmación de la hispanidad y que niegan su sentido emancipatorio, así como los recorridos biográficos de sus autores, revelan redes de sociabilidad intelectual que bajo la nominación de nacionalismo encubrían no pocas especificidades, al mismo tiempo que revelaban las vinculaciones existentes con la escuela historiográfica sevillana, por entonces usina intelectual del franquismo y nutriente del pensamiento nacionalista conservador y autoritario de los años sesenta.Research on the nationalism present in post- Peronism in Mendoza has allowed us to retrieve a number of intellectual itineraries that exemplify the complexity of a period in which the circulation and traffi c of ideas show not only strong identity mutation processes, but also the crystallization of undoubtedly anachronistic positions. In this article we aim to survey -in the context of the sesquicentennial of the May Revolution celebrations-, the important historical production that circulated in zones of wide diffusion, and which contributed to implant a powerful tradition that lasted for a considerable time in the local academic scene. Rather than explaining the impact that they had

  10. Seismic hazard reappraisal from combined structural geology, geomorphology and cosmic ray exposure dating analyses: the Eastern Precordillera thrust system (NW Argentina) (United States)

    Siame, L. L.; Bellier, O.; Sébrier, M.; Bourlès, D. L.; Leturmy, P.; Perez, M.; Araujo, M.


    Because earthquakes on large active thrust or reverse faults are not always accompanied with surface rupture, paleoseismological estimation of their associated seismic hazard is a difficult task. To improve the seismic hazard assessments in the Andean foreland of western Argentina (San Juan Province), this paper proposes a novel approach that combines structural geology, geomorphology and exposure age dating. The Eastern Precordillera of San Juan is probably one of the most active zones of thrust tectonics in the world. We concentrated on one major regional active reverse structure, the 145 km long Villicúm-Pedernal thrust, where this methodology allows one to: (1) constrain the Quaternary stress regime by inversion of geologically determined slip vectors on minor or major fault planes; (2) analyse the geometry and the geomorphic characteristics of the Villicúm-Pedernal thrust; and (3) estimate uplift and shortening rates through determination of in situ-produced 10Be cosmic ray exposure (CRE) ages of abandoned and uplifted alluvial terraces. From a structural point of view, the Villicúm-Pedernal thrust can be subdivided into three thrust portions constituting major structural segments separated by oblique N40°E-trending fault branches. Along the three segments, inversion of fault slip data shows that the development of the Eastern Precordillera between 31°S and 32°S latitude is dominated by a pure compressive reverse faulting stress regime characterized by a N110°+/- 10°E-trending compressional stress axis (σ1). A geomorphic study realized along the 18 km long Las Tapias fault segment combined with CRE ages shows that the minimum shortening rate calculated over the previous ~20 kyr is at least of the order of 1 mm yr-1. An earthquake moment tensor sum has also been used to calculate a regional shortening rate caused by seismic deformation. This analysis of the focal solutions available for the last 23 yr shows that the seismic contribution may be three

  11. Carbonate microfacies of the San Juan Formation (Ordovician: Oepikodus evae and Oepikodus intermedius conodont zones), Niquivil, Central Precordillera, Province of San Juan (Argentina)

    International Nuclear Information System (INIS)

    Soria, T.; Beresi, M.; Mestre, A.; Heredia, S.; Rodríguez, M.C.


    This contribution presents the description and interpretation of carbonate microfacies of the San Juan Formation (Ordovician) at the Niquivil section, considering the stratigraphical interval between the Oepikodus evae and Oepikodus intermedius conodont zones. The distribution of the microfacies and the conodonts assemblages allow us to identify different sub-environments within the late Floian carbonate ramp of the Central Precordillera. Five microfacies were recognized from the base to the top: M1 Bioclastic mudstone-wackestone; M2 Bioclastic-peloidal wackestone; M3 Intra-bioclastic wackestone; M4 Intra-bioclastic packstone; M5 Peloidal grainstone. The vertical distribution of these microfacies indicates a shallowing trend of the carbonate ramp in the Niquivil section for this temporal interval, which suggests a middle ramp environment with low energy, without wave action, and that evolved towards the middle-inner ramp environment with more energy by wave action and development of tempestites. [es

  12. The lower Darriwilian (Middle Ordovician) at the northern extreme of the Mendoza Precordillera, Argentina: stratigraphic and biostratigraphic implications; El Darriwiliense inferior (Ordovícico Medio) en el extremo norte de la Precordillera de Mendoza, Argentina: implicaciones estratigráficas y bioestratigráficas

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    Beresi, M.S.; Bordonaro, O.L.; Heredia, S.E.; Mestre, A.; Toro, B.A.


    A tectonically affected Middle Ordovician succession crops out at the Los Guanacos quarry in the sierra de Las Higueras, in the Precordillera of Mendoza, western Argentina. This is represented by the San Juan Formation which is transitionally covered by a mixed carbonate-shaly unit of dark colours, 1.5 metres thick (transfacies) which can be interpreted as the base of the Los Azules Formation. A 5-cm thick intra-bioclastic pack/grainstone bed interbedded in the lower part of this unit has been interpreted as a tempestite. It is characterized both by a millimetre-thick erosional boundary, just above the dark mudstone layer and strong mechanical distribution of bioclasts and intraclasts, suggesting sedimentary structures associated with a storm event of high energy possibly occurring in the middle part of the platform. Towards the bottom, a hummocky structure thin interval, under the dark mudstone, is interpreted as the record of another tempestite event. The mudstone represents the post-storm event reflecting the low energy of the marine water environment. The lenticular layer contains predominantly lingulid shells, trilobites and graptolites, all highly fragmented, which suggests they have been reworked and subsequently mixed and quickly redeposited during a storm event that caused the mortality of these faunas. The trilobites Mendolaspis salagastensis and indeterminate species of Matagnostidae, Illaenidae, Leiostegiidae, Encrinuridae, Telephinidae and Trinucleidae have been recorded for the first time at this locality. The conodont fauna allows the identification of the Yangtzeplacognathus crassus Zone, which indicates the lower Darriwilian (Middle Ordovician). Graptolites assignable to evisograptus cf. Levisograptus austrodentatus and Levisograptus sp. are described for the first time in the studied area and biostratigraphic implications validate the early Darriwilian age for the bearing levels. Finally, based on the studied records, correlation with different

  13. U-Pb and K-Ar geochronology from the Cerro Empexa Formation, 1st and 2nd Regions, Precordillera, northern Chile

    International Nuclear Information System (INIS)

    Tomlinson, A.J; Martin, M.W; Blanco, N.; Perez de Arce, C


    The Cerro Empexa Formation (Galli, 1957) is a regionally distributed andesitic volcanic and continental sedimentary unit exposed in the Precordillera of the 1st and 2nd Regions of northern Chile. The formation has generally been considered to lie within the Lower or 'mid' Cretaceous, however, this assignment is based on scant, unreliable geochronologic data. Furthermore, there are conflicting interpretations as to whether the unit predates or postdates the first major Mesozoic shortening event affecting northern Chile. Because of the formation's presumed mid-Cretaceous age and its stratigraphic position over older back-arc sedimentary successions, the unit has been interpreted to represent products of the first eastward jump in the Andean magmatic arc from the arc's initial position in the Cordillera de la Costa (Scheuber and Reutter, 1992). In this paper we present the results of mapping and field observations that indicate exposures previously assigned to the Cerro Empexa Formation include two andesitic volcanic units separated by a major unconformity. The Cerro Empexa Formation proper lies above this unconformity. We also present U-Pb zircon and K-Ar geochronology that indicate the Cerro Empexa Formation is latest Cretaceous in its lower levels, and integrate our data with previously reported 40 Ar/ 39 Ar and fission-track data in the Cerros de Montecristo area (Maksaev, 1990; Maksaev and Zentilli, 1999) to show that 1800±600 m of rocks were deposited within ca. 2.5 m.y (au)

  14. Vertical-axis rotations and deformation along the active strike-slip El Tigre Fault (Precordillera of San Juan, Argentina) assessed through palaeomagnetism and anisotropy of magnetic susceptibility (United States)

    Fazzito, Sabrina Y.; Rapalini, Augusto E.; Cortés, José M.; Terrizzano, Carla M.


    Palaeomagnetic data from poorly consolidated to non-consolidated late Cenozoic sediments along the central segment of the active El Tigre Fault (Central-Western Precordillera of the San Juan Province, Argentina) demonstrate broad cumulative deformation up to 450 m from the fault trace and reveal clockwise and anticlockwise vertical-axis rotations of variable magnitude. This deformation has affected in different amounts Miocene to late Pleistocene samples and indicates a complex kinematic pattern. Several inherited linear structures in the shear zone that are oblique to the El Tigre Fault may have acted as block boundary faults. Displacement along these faults may have resulted in a complex pattern of rotations. The maximum magnitude of rotation is a function of the age of the sediments sampled, with largest values corresponding to middle Miocene-lower Pliocene deposits and minimum values obtained from late Pleistocene deposits. The kinematic study is complemented by low-field anisotropy of magnetic susceptibility data to show that the local strain regime suggests a N-S stretching direction, subparallel to the strike of the main fault.

  15. The geometry of the active strike-slip El Tigre Fault, Precordillera of San Juan, Central-Western Argentina: integrating resistivity surveys with structural and geomorphological data (United States)

    Fazzito, Sabrina Y.; Cortés, José M.; Rapalini, Augusto E.; Terrizzano, Carla M.


    The geometry and related geomorphological features of the right-lateral strike-slip El Tigre Fault, one of the main morphostructural discontinuities in the Central-Western Precordillera of Argentina, were investigated. Achievements of this survey include: recognition of structural and geometrical discontinuities along the fault trace, identification and classification of landforms associated with local transpressional and transtensional sectors, observation of significant changes in the fault strike and detection of right and left bends of different wavelength. In the Central Segment of the El Tigre Fault, 2D electrical resistivity tomography surveys were carried out across the fault zone. The resistivity imaging permitted to infer the orientation of the main fault surface, the presence of blind fault branches along the fault zone, tectonic tilting of the Quaternary sedimentary cover, subsurface structure of pressure ridges and depth to the water table. Based on this information, it is possible to characterize the El Tigre Fault also as an important hydro-geological barrier. Our survey shows that the main fault surface changes along different segments from a high-angle to a subvertical setting whilst the vertical-slip component is either reverse or normal, depending on the local transpressive or transtensive regime induced by major bends along the trace. These local variations are expressed as sections of a few kilometres in length with relatively homogeneous behaviour and frequently separated by oblique or transversal structures.

  16. Carbonate microfacies of the San Juan Formation (Ordovician: Oepikodus evae and Oepikodus intermedius conodont zones), Niquivil, Central Precordillera, Province of San Juan (Argentina); Microfacies carbonáticas de la Formación San Juan (Ordovícico: zonas de conodontos Oepikodus evae y Oepikodus intermedius), Niquivil, Precordillera Central, Provincia de San Juan (Argentina)

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    Soria, T.; Beresi, M.; Mestre, A.; Heredia, S.; Rodríguez, M.C.


    This contribution presents the description and interpretation of carbonate microfacies of the San Juan Formation (Ordovician) at the Niquivil section, considering the stratigraphical interval between the Oepikodus evae and Oepikodus intermedius conodont zones. The distribution of the microfacies and the conodonts assemblages allow us to identify different sub-environments within the late Floian carbonate ramp of the Central Precordillera. Five microfacies were recognized from the base to the top: M1 Bioclastic mudstone-wackestone; M2 Bioclastic-peloidal wackestone; M3 Intra-bioclastic wackestone; M4 Intra-bioclastic packstone; M5 Peloidal grainstone. The vertical distribution of these microfacies indicates a shallowing trend of the carbonate ramp in the Niquivil section for this temporal interval, which suggests a middle ramp environment with low energy, without wave action, and that evolved towards the middle-inner ramp environment with more energy by wave action and development of tempestites. [Spanish] En la presente contribución se realiza la descripción e interpretación de las microfacies carbonáticas de la Formación San Juan (Ordovícico) en la sección de Niquivil, considerando el intervalo estratigráfico comprendido entre las zonas de conodontos Oepikodus evae y Oepikodus intermedius. El análisis de las microfacies y los conodontos asociados permiten el reconocimiento de diferentes subambientes carbonáticos dentro de la rampa carbonática desarrollada durante el Floiense tardío de la Precordillera Central. Se reconocieron cinco microfacies que, de base a techo, son: M1 Mudstone-Wackestone bioclástico; M2 Wackestone bioclástico-peloidal; M3 Wackestone intra-bioclástico; M4 Packstone intra-bioclástico; M5 Grainstone peloidal. La interpretación vertical de estas microfacies indica una tendencia hacia la somerización de la rampa carbonática en la sección de Niquivil para el lapso temporal estudiado. El que se correspondería con un ambiente de

  17. The Sanrafaelic remagnetization revisited: Magnetic properties and magnetofabrics of Cambrian-Ordovician carbonates of the Eastern Precordillera of San Juan, Argentina (United States)

    Fazzito, Sabrina Y.; Rapalini, Augusto E.; Poiré, Daniel G.


    Systematic rock-magnetic and magnetofabric studies were carried out on samples from twenty-three palaeomagnetic sites distributed on the La Laja, Zonda, La Flecha, La Silla and San Juan Formations, which constitute a thick middle Cambrian to early Ordovician carbonate sequence exposed in the Eastern Precordillera of Argentina. Previous palaeomagnetic studies on these rocks showed that this succession is characterized by a recent full overprint in the lower levels and a post-tectonic Permian remagnetization associated to the widespread Sanrafaelic event in the upper part. Our investigation revealed that the fluctuations of the magnetic properties are stratigraphically (lithologically) controlled. Anisotropy of magnetic and anhysteretic susceptibility measurements defined consistent fabrics along the entire section that switch progressively from "inverse", at the bottom, to "normal", at the top, with "intermediate" fabrics occurring mainly at medium levels. Degree of dolomitization significantly affects many rock-magnetic parameters, but appears unrelated to the presence of the Permian remagnetization, which is determined to reside in magnetite despite the complex magnetic mineralogy shown by the studied carbonates. Hysteresis cycles of rocks affected by the Sanrafaelic remagnetization are governed by ferromagnetic fractions showing a clear difference respect to those not affected and characterized by the dominance of paramagnetic or diamagnetic signals. The magnetic fabrics and mineralogical characterization rule out a thermoviscous origin and suggest a chemical remagnetization originated in the authigenic formation of magnetite for the Sanrafaelic overprint. X-ray diffraction analyses indicate that clay minerals are virtually absent in the whole succession with no traces of illite in any sample, discarding burial diagenesis of clay minerals for the origin of the remagnetization. Lack of late Palaeozoic magmatic rocks near the study area difficults correlation of

  18. Estructura del borde occidental de la Precordillera, en el área comprendida entre la Sierra del Tontal y el río Castaño, desde el río San Juan hasta la base del Cerro Colorado


    Selles Martinez, José


    El estudio estructural de las unidades del Paleozoico inferior y medio del borde occidental de la Precordillera ha sido demorado durante largo tiempo debido a la complejidad de las estructuras presentes, a la superposición de al menos tres episodios deformativos y a la dificultad para identificar y separar las diferentes unidades aflorantes, muy semejantes todas en algunos tramos de su perfil. En el presente trabajo se señalan las características estructurales más importantes de las secuencia...

  19. La Formación Los Llantenes en la Precordillera de Jagüé (La Rioja y la identificación de un episodio de extensión en la evolución temprana de las cuencas del Paleozoico superior en el oeste argentino The Los Llantenes Formation in the Precordillera of Jagüé (La Rioja Province and the recognition of a rifting stage in the early evolution of the late Paleozoic basins in western Argentina

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    Ricardo A Astini


    Full Text Available En la región septentrional de la Precordillera, al NW de La Rioja, en el centro occidental de Argentina, afloran más de 4.000 m de rocas sedimentarias del Paleozoico superior entre las que se destaca una unidad basal psefítica, no descrita con anterioridad y cuyo análisis permite identificar un importante episodio de extensión cortical. El potente conglomerado (>1.000 m de color morado, que proponemos denominar Formación Los Llantenes, se dispone en no concordancia sobre el basamento de la Precordillera Septentrional y por debajo del primer nivel con clara impronta glacigénica, asociado a la glaciación gondwánica. Mientras que su gran espesor y escasa distribución areal indican subsidencia localizada, la estratofábrica cruda, la mala selección granulométrica y la presencia de bloques superiores al metro indicarían que se trata de depósitos de abanicos aluviales de alto gradiente, dominados por flujos de gravedad. Su composición y granulometría gruesa revelan procedencia local, resaltos topográficos pronunciados y fuerte compartimen-tación paleogeográfica. Una compleja historia glacial sucede a la Formación Los Llantenes sobre la que se han labrado profundos paleovalles en forma de 'U' que alojan tilitas y diamictitas glacigénicas, pertenecientes a la Formación Cerro Tres Cóndores de edad viseana (Misisipiano Medio. La edad de los conglomerados de la Formación Los Llantenes, de naturaleza preglacial, quedaría acotada entre el sustrato del Devónico Medio, aflorante inmediatamente al sur de la región estudiada en sierra de Las Minitas, y el Misisipiano Medio (Formación Cerro Tres Cóndores, pudiendo parcialmente constituir un equivalente de la Formación Agua de Lucho (Tournaisiano-Viseano que, en la región del Río del Peñón, también subyace a los niveles glacigénicos de la Formación Cerro Tres Cóndores. La expresión cartográfica con limitada extensión areal y el gran espesor que presentan las psefitas de la

  20. The chromium isotopic composition of an Early to Middle Ordovician marine carbonate platform, eastern Precordillera, San Juan, Argentina

    DEFF Research Database (Denmark)

    D'Arcy, Joan Mary; Frei, Robert; Gilleaudeau, Geoffrey Jon

    A broad suite of redox proxy data suggest that despite ocean and atmosphere oxygenation in the late Neoproterozoic, euxinic conditions persisted in the global deep oceans until the at least Ordovician [1,2,3]. Major changes in the sulphur isotopic composition of carbonate associated sulphate and ...

  1. Significado estratigráfico y tectónico de los complejos de bloques resedimentados cambro-ordovicios de la Precordillera Occidental, Argentina

    Directory of Open Access Journals (Sweden)

    Vaccari, N. E.


    Full Text Available Rocks belonging to the Early Paleozoic Los Sombreros Formation crop out on the eastern flank of the Sierra de Yerba Loca, along the Río Jáchal section. This Formation consists of black shales and turbidites with interbedded limestone boulders near the base of the section, one of them up to 200 m long and 30 m thick. Boulders yield both early Cambrian trilobites and early Ordovician conodonts. Near the top, a thick sequence of dark grey marls and limestone contains an early Middle Cambrian trilobite fauna which is overlain by limestone and calcareous turbidites containing early Llanvirn graptolites and conodonts. On the basis of paleontological and sedimentological evidences this sequence can be interpreted as a series of submarine gravity slides interbedded within a dominantly turbiditic sequence. The Cambrian-early Ordovician precordilleran carbonate platform served as the source for much of the sediment which was redeposited on the slope. Then, deposition of the early Ordovician Los Sombreros Formation could be related to uplift and erosion of the platform margin and steeping of the slope during the late Arenig-early Llanvirn.En el flanco oriental de la Sierra de Yerba Loca, sobre el corte del río Jáchal, aflora una secuencia de edad paleozoica temprana correspondiente a los afloramientos más septentrionales de la Formación Los Sombreros. Esta unidad se compone de lutitas negras y turbiditas que contienen cerca de su base y hacia el techo horizontes de bloques calcáreos, algunos de enormes dimensiones -cerca de 30 m de espesor por más de 200 m de longitud- cuya fauna de trilobites y conodontos indica una edad Cámbrica y Ordovícica temprana. Hacia el techo de la sección está expuesta una potente secuencia de calcipelitas y calizas oscuras que contienen una fauna de trilobites del Cámbrico Medio basal, que es cubierta por brechas calcáreas y calciturbiditas portadoras de conodontos y graptolitos de edad llanvirniana temprana. Esta secuencia mesocámbrica es interpretada también como un bloque olistolítico. Sobre la base de las evidencias paleontológicas y sedimentológicas se interpreta que la Formación Los Sombreros se habría originado a partir de una serie de deslizamientos gravitacionales submarinos dentro de una secuencia dominantemente turbidítica. La plataforma cámbrica y eo-ordovícica precordillerana fue la fuente de la mayor parte de los sedimentos que fueron redepositados sobre el talud. La sedimentación de la Formación Los Sombreros sería el resultado de la flexura y erosión del borde de la plataforma carbonática asociado a un brusco aumento de la pendiente del talud durante el Arenigiano tardío-Llanvirniano temprano.


    Directory of Open Access Journals (Sweden)

    O. S. Vallejos-Barra


    Full Text Available En este estudio se comparó el comportamiento de un bosque secundario de Roble-Hualo, donde las especies predominantes son Nothofagus obliqua y Nothofagus glauca y una plantación de Pinus radiata D. Don de 12 años de edad, en el proceso precipitación - intercepción. El estudio se desarrolló en la Estación Experimental El Picazo, comuna de San Clemente, Región del Maule, Chile, entre el mes de julio de 2007 a julio de 2008, en dos microcuencas vecinas de dimensiones reducidas con condiciones similares de suelo, exposición y pendiente pero que diferían en la cobertura vegetal. Se caracterizó la vegetación de cada microcuenca y se establecieron indicadores de densidad de parcela. Los indicadores de la cobertura nativa superaron ampliamente a los de las coberturas exóticas. Para registrar la precipitación se instalaron dos pluviógrafos del tipo Hobo en cada microcuenca. Equidistante de ellas se ubicó otro pluviógrafo sin cobertura vegetal. Se registraron 21 tormentas caracterizando temporal y espacialmente el comportamiento de la precipitación abierta y bajo dosel. Los resultados indican que pese a tener diferencias numéricas las coberturas vegetales, éstas no se transforman en diferencias estadísticamente significativas. Además se observó que la intercepción depende en mayor medida de la arquitectura de copa, distribución espacial de los árboles y tipo de hojas, que de la cantidad de árboles por parcela.

  3. Morphotectonic and neotectonic control on river pattern in the Sierra de la Cantera piedmont, Central Precordillera, province of San Juan, Argentina (United States)

    Perucca, Laura P.; Rothis, Martín; Vargas, Horacio N.


    The drainage pattern on the western piedmont of the Sierra de La Cantera is divergent, typical of alluvial fans and showing anomalies that are directly related to the trace of La Cantera thrust. In previous studies, two types of anomalies were identified: upstream of the fault scarp, rivers have a broom-shaped pattern, while downstream - in the hanging block - streams become denser, more sinuous and incised. In this contribution, these morphotectonic aspects were analyzed in detail, making direct and indirect analysis to quantify the relationship between these anomalies and the faults affecting alluvial fans. In addition, the influence of neotectonic activity on smaller water course patterns in the alluvial fan areas was investigated in order to find indicators of on-going vertical movements, since the spatial arrangements of these piedmont channels are determined by slope and structure, where active faults cause diversions or anomalies. Topographic profiles in two selected channels cutting across the trace of the fault were performed using a differential GPS in order to establish the relationship between the sinuosity and slope of these rivers. The results obtained allow us to state that the most sinuous channels have lower slopes and are located in the hanging wall of the fault. Morphometric analysis of scarps stated that active tectonics have played an essential role in controlling the drainage pattern in the piedmont, leading the rivers to adjust to these slope variations. Finally, based on the geomorphologic, stratigraphic, structural and seismological characteristics and parameters analyzed, La Cantera Thrust is considered a seismogenic source of significance to the nearby towns (> 700,000 inhabitants) and also to the large-scale dams built downstream along the San Juan River.

  4. Dissolution of Fe(III)(hydr)oxides by an Aerobic Bacterium

    International Nuclear Information System (INIS)

    Maurice, P.


    This project investigated the effects of an aerobic Pseudomonas mendocina bacterium on the dissolution of Fe(III)(hydr)oxides. The research is important because metals and radionuclides that adsorb to Fe(III)(hydr)oxides could potentially be remobilized by dissolving bacteria. We showed that P. mendocina is capable of dissolving Fe-bearing minerals by a variety of mechanisms, including production of siderophores, pH changes, and formation of reductants. The production of siderophores by P. mendocina was quantified under a variety of growth conditions. Finally, we demonstrated that microbial siderophores may adsorb to and enhance dissolution of clay minerals

  5. Notas taxonómicas en Asteraceae

    Directory of Open Access Journals (Sweden)

    Adriana Bartoli


    Full Text Available Se describe una nueva variedad para Grindelia anethifolia y se amplía el área de distribución de Bidens andicola, Grindelia coronensis y Proustia cuneifolia var. mendocina.Taxonomic notes on Asteraceae. A new variety for Grindelia anethifolia is described, and the known area of Bidens andicola, Grindelia coronensis and Proustia cuneifolia var. mendocina is extended.

  6. Isolation and characterization of two malathiondegrading ...

    African Journals Online (AJOL)

    Pseudomonas aeruginosa and Pseudomonas mendocina degrading malathion were studied. Morphological, biochemical and 16S rRNA genes for bacterial identification were selected. Biodegradation of some organophosphorus compounds with the 2 bacterial isolates was determined by high performance liquid ...

  7. Uplift sequence of the Andes at 30°S: Insights from sedimentology and U/Pb dating of synorogenic deposits (United States)

    Suriano, J.; Mardonez, D.; Mahoney, J. B.; Mescua, J. F.; Giambiagi, L. B.; Kimbrough, D.; Lossada, A.


    The South Central Andes at 30°S represent a key area to understand the Andes geodynamics as it is in the middle of the flat slab segment and all the morphotectonic units of the Central Andes are well developed. This work is focused in the proximal synorogenic deposits of the Western Precordillera, in the La Tranca valley, in order to unravel the uplift sequence of this belt. Nine facies associations were recognized; most of them represent piedmont facies with local provenance from Precordillera and were deposited in the wedge-top depozone, as is expected for proximal sinorogenic deposits. However there are intercalations of transference fluvial systems, which show mixed provenance indicating that Permo-Triassic igneous rocks were already exposed to the west (Frontal Cordillera). There are also lacustrine deposits which are interpreted as the result of damming by fault activity at east of the studied basin. Finally, two maximum depositional ages at ca. 11 Ma and 8 Ma of these deposits indicate that the onset of uplift of the Precordillera at 30°S is little older than 11 Ma. These data change two previous ideas about the evolution of the Precordillera: its uplift at 30° S is younger than proposed by previous works and it is nearly synchronous along strike.

  8. ESTUDIO ARQUEOHISTÓRICO DEL REGISTRO VÍTREO EN SITIOS MINEROS (MENDOZA, ARGENTINA (Archaeohistorical Study of the Vitreous Record in Mining Sites (Mendoza, Argentina

    Directory of Open Access Journals (Sweden)

    Osvaldo Sironi


    Full Text Available Se presentan los resultados de los análisis de los registros vítreos de los sitios Minas Paramillos Sur y Mina La Atala, localizados en la Reserva Natural Villavicencio y Divisadero Largo. A partir del conocimiento de la materialidad cultural vítrea de esta región, se evidencian patrones de consumo vinculados a diversos tipos de bebidas y productos medicinales entre la clase trabajadora minera de la Precordillera de Mendoza (Argentina. ENGLISH: Results of the analysis of the vitreous record from Minas Paramillos Sur and Mina La Atala are presented. These sites are located in the Villavicencio and Divisadero Largo natural reserves. Knowledge of the vitreous cultural material of this region allows us to show consumption patterns of various types of beverages and medicines among the mining working class of the Mendoza Precordillera, Argentina.

  9. Seismotectonics of thin- and thick-skinned deformation in the Andean foreland from local network data - Evidence for a seismogenic lower crust (United States)

    Smalley, Robert, Jr.; Isacks, Bryan L.


    Local network data from San Juan, Argentina, provides new information about crustal seismicity in the Andean foreland above a horizontal segment of the subducted Nazca Plate. Two areas of foreland seismicity are found, one associated with the Sierras Pampeanas basement uplifts, and the other beneath, but not within, the Precordillera foreland fold-thrust belt. The Precordillera seismicity provides direct evidence for basement deformation beneath the sediments of the thrust belt and supports the idea that its eastern part is significantly modified by underlying basement deformation. In both areas, events are concentrated between 15 and 35 km depth and have volumetric, rather than planar, faultlike distributions. The depth distribution is unusually deep for intraplate earthquakes and suggests a brittle-ductile transition near 30-35 km.

  10. Diagnóstico microbiológico e histopatológico de mortalidade em avestruzes (Struthio camelus Microbiological and histological diagnosis in mortality of ostrich (Struthio camelus

    Directory of Open Access Journals (Sweden)

    O. Vieira-da-Motta


    Full Text Available Several young ostrich, including nestlings, with lassitude and inappetence followed by death or victim of sudden death were immediately brought to diagnosis at an Animal Health Laboratory. At necropsy, animals presented hemorrhage and altered content of the vitelline sac, and necrotic foci in the small intestine; one animal showed necrotic pleuropneumonia with psammomatosus bodies in the lung parenchyma. The cultures from different samples revealed Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Serratia marcescens, Enterobacter aglomerans, and Pseudomonas mendocina. It was suggested one case of septicemia in an animal with exclusive growth of K. pneumoniae isolated from samples of small intestine, lung, and liver.


    Directory of Open Access Journals (Sweden)

    José C. Mendoza


    Full Text Available Fue estudiada la biodegradación de permetrina y cipermetrina a concentraciones de 50 y 100 mg/L, con cepas de Pseudomonas putida, Pseudomonas mendocina, Chromobacterium violaceum y Burkholderia cepacia, en reactores por lotes. Las cepas de Pseudomonas putida y Pseudomonas mendocina fueron las que presentaron una mayor capacidad de biodegradación de los plaguicidas, a partir de los 5 días esta es del 65% para ambos plaguicidas y después de los 15 días se mantiene prácticamente constante, siendo de hasta el 95% para permetrina a 50 y 100 mg/L y para cipermetrina del 90% a 50 mg/L y 89% a 100 mg/L medido mediante espectrofotometría UV/Vis. La cinética de crecimiento y los espectros de infrarrojo muestran que hay una mayor capacidad de mineralización para el plaguicida permetrina que para la cipermetrina. Estos resultados indican que estas bacterias pueden ser usadas en procesos de biorremediación de estos plaguicidas.

  12. 3-D velocity structures, seismicity patterns, and their tectonic implications across the Andean Foreland of San Juan Argentina (United States)

    Asmerom, Biniam Beyene

    Three-dimensional velocity structures and seismicity patterns have been studied across the Andean Foreland of San Juan Argentina using data acquired by PANDA deployment. Distinct velocity variations are revealed between Precordillera in the west and Pie de Palo in the east. The low velocity anomaly beneath Precordillera is associated with the presence of thick sedimentary rocks and thick sediment cover of Matagusanos valley. Similarly, the high velocity anomaly east of Eastern Precordillera is correlated with the presence of basement rocks. These anomalies are observed from the station corrections of Joint Hypocentral Determination (JHD) analysis. A northeast trending west dipping high velocity anomaly is imaged beneath the southern half of Pie de Palo. This anomaly represents a Grenvillian suture zone formed when Pie de Palo collided with the Precordillera. Relocated seismicity using 3-D Vp and Vs models obtained in this study revealed crustal scale buried faults beneath the Eastern Precordillera and Sierra Pie de Palo. The fault defined by the seismicity extend down to a depth of ˜ 40 km and ~35 km beneath Precordillera and Pie de Palo, respectively, defining the lower bound of the brittle to ductile transition of the crust. These results confirm that present day active crustal thickening involves the entire crust in the tectonic process and results in thick-skinned deformation beneath both the Eastern Precordillera and Pie de Palo. Based on the seismicity pattern, geomorphology, and velocity structures, Sierra Pie de Palo, a basement uplift block, can be divided into two separate semi-blocks separated by a northeast trending fracture zone. The northern block is characterized by a well-defined west dipping fault and low Vp/Vs ratio particularly at a depth of 12 to 16 km, while the southern block shows a poorly-defined east dipping fault with high Vp/Vs ratio at a depth of 20 to 26 km. Spatial distribution of the well-relocated crustal earthquakes along these

  13. Insights into Andean slope hydrology: reservoir characteristics of the thermal Pica spring system, Pampa del Tamarugal, northern Chile (United States)

    Scheihing, Konstantin W.; Moya, Claudio E.; Tröger, Uwe


    The thermal Pica springs, at ˜1,400 m above sea level (asl) in the Pampa del Tamarugal (Chile), represent a low-saline spring system at the eastern margin of the hyper-arid Atacama Desert, where groundwater resources are scarce. This study investigates the hydrogeological and geothermal characteristics of their feed reservoir, fostered by the interpretation of a 20-km east-west-heading reflection-seismic line in the transition zone from the Andean Precordillera to the Pampa del Tamarugal. Additional hydrochemical, isotope and hydrologic time-series data support the integrated analysis. One of the main factors that enabled the development of the spring-related vertical fracture system at Pica, is a disruption zone in the Mesozoic Basement caused by intrusive formations. This destabilized the younger Oligocene units under the given tectonic stress conditions; thus, the respective groundwater reservoir is made up of fractured Oligocene units of low to moderate permeability. Groundwater recharge takes place in the Precordillera at ˜3,800 m asl. From there groundwater flow covers a height difference of ˜3,000 m with a maximum circulation depth of ˜800-950 m, where the waters obtain their geothermal imprint. The maximal expected reservoir temperature, as confirmed by geothermometers, is ˜55 °C. Corrected mean residence times of spring water and groundwater plot at 1,200-4,300 years BP and yield average interstitial velocities of 6.5-22 m/year. At the same time, the hydraulic head signal, as induced by recharge events in the Precordillera, is transmitted within 20-24 months over a distance of ˜32 km towards the Andean foothills at Pica and Puquio Nunez.

  14. Conflictos socio-ambientales/territoriales y el surgimiento de identidades post neoliberales (Valparaíso-Chile)


    Bolados García, Paola


    Resumen: En este artículo analizamos los conflictos socio-ambientales/territoriales asociados a la expansión de las fronteras minera y agroexportadora en la zona central de Chile. Nos centramos en el conflicto por la usurpación del agua en la precordillera de la Provincia de Petorca, así como los conflictos asociados a la contaminación producida por el Complejo Industrial Ventanas en los límites de las comunas de Puchuncaví y Quintero. Desde una perspectiva crítica que se nutre de la ecología...



    Poblete S,María Pía


    El propósito de este artículo es indagar en las percepciones y valoraciones de la experiencia escolar en un contexto interétnico. Presentamos información proveniente de 30 relatos sobre la educación y la experiencia escolar de personas mapuches de la precordillera de la Comuna de Panguipulli. Los resultados nos muestran que las experiencias en la escuela estuvieron marcadas por la discriminación étnica en la mayoría de los entrevistados. La discriminación se vivió en la interacción con profes...

  16. A new genus of Platynini (Coleoptera: Carabidae) from Argentina


    ROIG-JUÑENT, Sergio


    Los Platynini constituyen un grupo de carábidos distribuidos ampliamente en América del Sur, existiendo la mayor diversidad de especies en las regiones tropicales de altura de Los Andes. En la Argentina y Chile, la mayoría de las especies de Platynini se hallan distribuidas en áreas extracordilleranas, conociéndose pocos datos para la región Andina. A partir de recolecciones realizadas en la Precordillera y Cordillera de los Andes en Mendoza (Argentina), se hallaron ejemplares pertenecientes ...

  17. Aporte a la geología del Alto de Mogna, al norte de la depresión del Tulum, provincia de San Juan A contribution to the Geology of the Mogna High, to the North of the Tulum depression, Province of San Juan


    J.J. Zambrano; G. Suvires


    El Alto de Mogna, elevación estructural situada en la parte central de la provincia de San Juan, entre las provincias geológicas de las Sierras Pampeanas y la Precordillera Oriental, tiene rumbo este-oeste, transversal a las estructuras de las mencionadas cadenas montañosas, y separa dos depresiones tectónicas regionales: el valle del Bermejo, al norte, y la depresión de Tulum, al sur. En esta elevación estructural afloran fallas y pliegues, cuyo rumbo es prácticamente este-oeste, salvo en la...

  18. Aporte a la geología del Alto de Mogna, al norte de la depresión del Tulum, provincia de San Juan


    J.J. Zambrano; G. Suvires


    El Alto de Mogna, elevación estructural situada en la parte central de la provincia de San Juan, entre las provincias geológicas de las Sierras Pampeanas y la Precordillera Oriental, tiene rumbo este-oeste, transversal a las estructuras de las mencionadas cadenas montañosas, y separa dos depresiones tectónicas regionales: el valle del Bermejo, al norte, y la depresión de Tulum, al sur. En esta elevación estructural afloran fallas y pliegues, cuyo rumbo es prácticamente este-oeste, salvo en la...

  19. Two new species of Psectrascelis (Coleoptera: Tenebrionidae from western Argentina

    Directory of Open Access Journals (Sweden)

    Gustavo E. FLORES


    Full Text Available Se describen dos nuevas especies del género Psectrascelis Solier (Pimeliinae: Nycteliini del oeste de Argentina, P. argentina sp. nov. a gran altitud en la Precordillera de San Juan y P. telteca sp. nov. en la llanura de Mendoza, y se las incluye en la clave mas reciente del género. Se proveen datos sobre la distribución y el hábitat, así como fotografías de los adultos y pronotos y dibujos de los genitalia masculinos.

  20. Geophysical evidence for an extensive Pie de Palo Complex mafic-ultramafic belt, San Juan, Argentina (United States)

    Chernicoff, Carlos J.; Vujovich, Graciela I.; van Staal, Cees R.


    The recent completion of a high-resolution aeromagnetic survey over the Pie de Palo uplift of the western Sierras Pampeanas has revealed an area of large magnetic anomalies associated with the Pie de Palo Complex. The Las Pirquitas thrust, which has transported and uplifted the Pie de Palo Complex, is recognized for at least 30 km in a roughly NE direction along the western boundary of the Pie de Palo Complex, beyond its limited outcrop. The type of sediments of the Caucete Group in the footwall of the Las Pirquitas thrust, which are regarded as the leading edge of the Precordillera terrane, are associated with much less pronounced magnetic anomalies. In addition, a conspicuous, NNE trending, broad magnetic high stands out in the survey, several kilometers to the east of the main outcrops of the Pie de Palo Complex; this broad magnetic anomaly bisects the Pie de Palo basement block, and continues further south at least as far as 32°S, the southern boundary of the latest aeromagnetic survey. This magnetic anomaly is interpreted to represent a structure corresponding to the Grenvillian Precordillera-Pie de Palo tectonic boundary zone, and would comprise the buried largest part of the mafic-ultramafic belt. The geophysical model of the magnetic data indicates that the boundary zone dips to the east, possibly suggesting the existence of a set of synthetic east dipping, west-verging thrusts, of which only one major structure (Las Pirquitas thrust) is exposed; the possibility of other slivers of upthrust boundary zone material cannot be excluded. It is considered that the Pie de Palo Complex represents a small sliver upthrust from the unexposed boundary zone material (containing highly magnetic mafic-ultramafic rocks). The east-dipping, west verging structures associated with the Pie de Palo Complex are suggested to represent an Ordovician reactivation of a Grenvillian suture zone developed when the Precordillera basement and Pie de Palo terrane docked; this

  1. Un género nuevo de Platynini (Coleoptera: Carabidae de la Argentina A new genus of Platynini (Coleoptera: Carabidae from Argentina

    Directory of Open Access Journals (Sweden)

    Sergio ROIG-JUÑENT


    Full Text Available Los Platynini constituyen un grupo de carábidos distribuidos ampliamente en América del Sur, existiendo la mayor diversidad de especies en las regiones tropicales de altura de Los Andes. En la Argentina y Chile, la mayoría de las especies de Platynini se hallan distribuidas en áreas extracordilleranas, conociéndose pocos datos para la región Andina. A partir de recolecciones realizadas en la Precordillera y Cordillera de los Andes en Mendoza (Argentina, se hallaron ejemplares pertenecientes a dos especies de dicha tribu de carábidos. El estudio de este material ha permitido establecer dos nuevas especies cuyos caracteres justifican su agrupación en un nuevo género, Austroglyptolenus nov. gen. La presencia de una carena dorsal en la protibia y el poseer la base del lóbulo medio esclerotizado agruparían a Austroglyptolenus nov. gen. con los géneros Glyptolenus Bates y Glyptolenoides Perrault. De ellos se diferencia por la forma de los metatarsitos, ausencia de diente en el saco interno y la presencia de un anillo de espículas en la bursa copulatriz. Por ello las especies de Austroglyptolenus nov. gen., A. mendozensis sp. nov. y A. precordillerae sp. nov. están más relacionadas con las especies de América del Sur tropical que con los Platynini australes extramontanos de la Argentina y Chile. En este aporte se proveen las descripciones e ilustraciones del género y de las nuevas especies, así como también claves para identificar los nuevos taxones.Platynini is a widespread tribe of carabids in South America, having the largest diversity of species in the tropical highlands of Andes. In Argentina and Chile, most of the platinine species are distributed in extra-Andean regions. Several specimens of platynine have been found in samples from the Precordillera and the Andes in Mendoza (Argentina. The study of these materials revealed two new species, whose characters justify the creation of a new genus, Austroglyptolenus gen. nov. The

  2. Slope instabilities along the Western Andean Escarpment and the main canyons in Northern Chile (United States)

    Crosta, G.; Hermanns, R. L.; Valbuzzi, E.; Dehls, J.; Yugsi Molina, F. X.; Sepulveda, S.


    The western slope of the Andes of northern Chile - southern Perù is generally subdivided from the west to the east into the morphological units of: the Coastal Cordillera, Central Depression, the Western Escarpment-Precordillera and the Western Andean Cordillera. The western escarpment and Precordillera are formed by the Azapa coarse-grained clastic formation (sandstones, conglomerates, mudstones) and the Oxaya (rhyodacitic ignimbrites) and Diablo volcanoclastic formations (Oligocene and Miocene). Important uplift has been suggested between the deposition of the Oxaya and Diablo formations. The entire area has been characterized by a long-term hyperaridity (Atacama desert), initially established between 20 and 15 Ma, and this caused a strong difference between the long term continuous uplift and low denudation rates. This long sector of the central western escarpment and Precordillera is incised by deep canyons and subparallel drainage network in the upper part. The drainage network developed in two main phases: a lower-middle Miocene phase with formation of a parallel poorly structured drainage network cutting into the Oxaya formation, and presently well preserved; the canyons have been incised in the initial topography starting around 9 Ma and up to about 3.8 Ma with subsequent refilling episodes. Valley incision (ave. rate of 0.2 mm yr-1) has been controlled by topographic uplift and less arid climate (after 7 Ma). As a consequence of these geologic and climatic settings the evolution of this area has been characterized by canyon incision and extremely large slope instabilities. These slope instabilities occur in the "interfluvial" sectors of the western escarpment and Precordillera and along the canyon flanks. Landslides affecting the preserved paleosurfaces, interested by the parallel drainage network in the Oxaya formation, involve volumes of various cubic kilometres (Lluta collapse, Latagualla Landslide) and can control the drainage network. These mega

  3. U-Pb geochronology of modern river sands from the flat-slab segment of the southern central Andes, Argentina, 29-31°S: Implications for Neogene foreland and hinterland basin evolution (United States)

    Capaldi, T.; Horton, B. K.; McKenzie, R.; Stockli, D. F.


    This study investigates how Andean river sediments in the flat-slab segment of western Argentina record active mixing of lithologically and geochemically distinct source regions comprising the Principal Cordillera, Frontal Cordillera, Precordillera fold-thrust belt, Sierras Pampeanas basement uplifts, and recycled Neogene basin fill. Detrital zircon U-Pb geochronological results for modern river sands discriminate variations from hinterland source regions, through river tributaries and main trunks of the Bermejo, Jachal, San Juan, and Mendoza rivers, and their respective fluvial megafans within the active foreland basin. Proportions of proximal zircon populations in the hinterland trunk rivers (with extensive Permian-Triassic and Cenozoic igneous exposures) diminish downstream with progressive contributions from the frontal Precordillera fold-thrust belt (dominantly Paleozoic sedimentary rocks) and Pampean basement uplifts. However, this systematic downstream dilution is perturbed in several catchments by significant recycling of older foreland basin fill. The degree of recycling depends on the position and extent of Oligocene-Pliocene exposures within the catchments. To discern the effects of the variable detrital zircon sources, multiple statistical methods are utilized. Quantitative comparisons suggest that variations in detrital zircon age distributions among the modern sands, and with older foreland basin fill and exposed bedrock, are dependent on spatial and temporal variations in exhumation and drainage network evolution within their respective Andean catchments. The present surface area of competing source regions and the configuration of hinterland tributary rivers largely dictate the degree of downstream dilution and/or recycling. This study provides a modern analogue and baseline for reconstructing Neogene shifts in foreland basin provenance, depositional systems, and drainage configurations during a critical transition to flat-slab subduction.

  4. Evaluation of pyrrolidonyl arylamidase for the identification of nonfermenting Gram-negative rods. (United States)

    Bombicino, Karina A; Almuzara, Marisa N; Famiglietti, Angela M R; Vay, Carlos


    To evaluate the activity of pyrrolidonyl arylamidase (PYR) for the differentiation and identification of nonfermenting gram negative rods (NFGNR), 293 isolates were tested. A 24 h culture of each test organism was prepared. From this a 108-109 cfu/mL suspension was added to 0.25 mL of sterile physiologic solution. A PYR disk was then added and the test was incubated for 30 minutes at 35-37 degrees C, at environmental atmosphere. Reading was done by adding 1 drop of cinnamaldehyde reagent. Strains of Acinetobacter baumannii, Acinetobacter haemolyticus, Alcaligenes faecalis, Bergeyella zoohelcum, Bordetella bronchiseptica, Bordetella hinzii, Brevundimonas diminuta, Brevundimonas vesicularis, Brucella ovis, Brucella spp., Brucella suis, Burkholderia cepacia complex, Moraxella catarrhalis, Moraxella lacunata, Moraxella nonliquefaciens, Moraxella osloensis, Oligella ureolytica, Pseudomonas alcaligenes, Pseudomonas mendocina, Pseudomonas pseudoalcaligenes, Pseudomonas putida, Pseudomonas stutzeri, Pseudomonas Vb3, Psychrobacter phenylpyruvicus, and Stenotrophomonas maltophilia were PYR negative. On the other hand Achromobacter piechaudii, Achromobacter denitrificans, Achromobacter xylosoxidans, Burkholderia gladioli, Chryseobacterium gleum-indologenes, Comamonas testosroni, Cupriavidus pauculus, Delftia acidovorans, Elizabethkingia meningoseptica, Myroides spp., Ochrobactrum anthropi, Pseudomonas oryzihabitans, Ralstonia pickettii, Rhizobium radiobacter, Shewanella spp., Sphingobacterium multivorum, Sphingobacterium spiritivorum, and Weeksella virosa were PYR positive. Finally, Acinetobacter lwoffii, Pseudomonas aeruginosa, Pseudomonas fluorescens, Roseomonas spp., and Sphingomonas paucimobilis-parapaucimobilis were PYR variable. PYR testing should be considered as a useful tool to facilitate the identification of NFGNR.

  5. Justicia de proximidad, estrategias patrimoniales y capital simbólico : El caso de José Pescara, jurisdicción de Mendoza, Río de la Plata, 1762-1823

    Directory of Open Access Journals (Sweden)

    Eugenia Molina


    Full Text Available La trayectoria de José Pescara, labrador y hacendado mendocino que logró no sólo edificar un amplio patrimonio familiar sino ejercer una serie de funciones en la justicia menor de la campaña mendocina, sirve de mirador para reflexionar sobre, al menos, dos cuestiones. Por una parte, acerca de las diversas formas a través de las cuales ciertos advenedizos lograron integrarse exitosamente en las élites tardocoloniales y revolucionarias rioplatenses. Por otra, respecto de la experiencia de la justicia de proximidad, a la vez como reconocimiento de prominencia y recurso para la acumulación de capital simbólico. La hipótesis de trabajo sostiene que las responsabilidades judiciales ejercidas por Pescara dieron cuenta de su incorporación en una trama de relaciones privilegiadas concentradas en el cuerpo de vecinos representados por el cabildo, pero también de que la justicia de proximidad ocupó un rol relevante en su propia estrategia de reproducción de su patrimonio familiar.

  6. Biodiesel production from waste cooking oil in a magnetically fluidized bed reactor using whole-cell biocatalysts

    International Nuclear Information System (INIS)

    Chen, Guanyi; Liu, Jing; Yao, Jingang; Qi, Yun; Yan, Beibei


    Highlights: • A MFBR system was used for biodiesel production from waste cooking oil. • Reaction parameters were optimized by response surface methodology. • Transesterification using MWCBs in MFBR obtained a max yield of 91.8% after 48 h. • The MWCBs can be reused in MFBR for 10 cycles with maintaining 87.5% yield. • The MFBR using MWCBs was an efficient system for large-scale biodiesel industry. - Abstract: Biodiesel production from catalytic transesterification of waste cooking oil (WCO) was investigated in a magnetically fluidized bed reactor (MFBR) over Pseudomonas mendocina cells immobilized in magnetic microspheres. The effects of methanol to oil molar ratio (MOMR), magnetic field intensity, biocatalysts concentration and reactant flow rate on biodiesel production were investigated. Optimization of the selected parameters was carried out for maximum biodiesel production using response surface methodology with support of Design-Expert software. The parameters optimized with response surface methodology were MOMR of 3.74:1, magnetic field intensity of 136.63 Oe, biocatalysts concentration of 10.21 wt.% and reactant flow rate of 16.97 mL/min. An experimental biodiesel yield of 91.8% was obtained at 35 °C after 48 h with these optimized parameters. Moreover, the magnetic whole-cell biocatalysts (MWCBs) exhibited good reusability in MFBR that 87.5% biodiesel yield could still be achieved after 10 cycles. The results suggested that MWCBs catalyzed transesterification in the MFBR system would have broad application prospects in biodiesel production.

  7. Arrowleaf Clover (Trifolium vesiculosum Savi: A New Species of Annual Legumes for High Rainfall Areas of the Mediterranean Climate Zone of Chile Trébol Vesiculoso (Trifolium vesiculosum Savi: Una Nueva Especie de Leguminosa Anual para Áreas de Alta Precipitación en la Zona Mediterránea de Chile

    Directory of Open Access Journals (Sweden)

    Carlos Ovalle M


    Full Text Available The present review examines the main attributes and agronomic characteristics of arrowleaf clover (Trifolium vesiculosum Savi and its incorporation into production systems in dryland areas of the Andean foothills of the humid Mediterranean climate zone of Chile. It is a new species of annual legume in Chile for light and medium textured soils. The root system can reach a depth of 1.5 m and its seeds have a high percentage of hardseedness (99.8%. It is an upright plant, with purplish-white flowers. The mature plant has large arrow-shaped leaves up to 50 mm long, often marked with a large white “V”. Dry matter and seed production in the Andean foothills is high (3.9-8.8 t DM ha-1 and 700-900 kg ha-1, respectively, surpassing the productivity of sub clover (Trifolium subterraneum L. cv. Mount Barker and crimson clover (Trifolium incarnatum L.. However, DM production in the second year was lower, possibly because the high percentage of hardseedness inhibited plant emergence. The phenological records and productive performance suggest that arrowleaf clover could contribute to improving pastoral production in dryland areas with annual rainfall levels of more than 800 mm, such as the Andean foothills in the central-southern region of Chile.En la presente revisión se examinan los principales atributos y características agronómicas del trébol vesiculoso (Trifolium vesiculosum Savi y su eventual incorporación a sistemas de producción en la precordillera andina de la zona de clima mediterráneo húmedo de Chile. Se trata de una nueva especie de leguminosa forrajera anual para suelos de textura liviana y media. El sistema radical puede alcanzar 1,5 m de profundidad y las semillas tienen un alto porcentaje de dureza seminal (99,8%. Es una planta de crecimiento erecto, flores de color blanco con una leve coloración púrpura. Las plantas adultas tienen grandes hojas con forma de flecha de más de 50 mm de largo, a menudo muestran una marca blanca en

  8. On the Relationship of Dynamic Forearc Processes in Southern Peru to the Development and Preservation of Andean Topography (United States)

    Hall, S. R.; Farber, D. L.; Audin, L.; Saillard, M.; Finkel, R. C.


    After more than 40 years of study, the timing and nature of Andean uplift remains an area of great scientific debate. The forearc of the Andean margin is of particular neotectonic interest, as previous models of Andean orogenesis attributed little-no Neogene deformation to the western margin of Altiplano. However, using the combination of remote sensing with high-resolution data, in situ cosmogenic isotope concentrations and thermochronology, in recent years the community has made important advances in addressing the rates, timings, styles, and locations of active deformation within the forearc of the Andean margin. To first order, we find that - both in terms of tectonics and climate - since 10Ma, the Andean forearc has been quite a dynamic region. Neotectonic studies in this region have been facilitated by the high degree of geomorphic surface preservation that the hyperarid (for at least the last 3My) coastal Atacama Desert has provided. Specifically, in southern Peru (14°-18°S), vast pediment surfaces have been abandoned through incision along the major river drainages that carve the deep canyons into the Precordillera and Western Cordillera. While the exact timing of the periods of more intense incision plausibly correspond with climate events, the total amount of incision integrated over many climate cycles is a useful indicator of tectonic activity. In this region, we find a number of geomorphic and structural features that provide strong evidence for distributed crustal deformation along range-sub-parallel contractile and strike-slip structures. Specifically, we see 1) ancient surfaces reflecting erosion rates as low as chronologies, and 6) Pleistocene mass-wasting events accommodating the redistribution of ~109-1010 m3 of material per event. Furthermore, the observation that Pleistocene incision rates are comparable with Late Miocene and Pliocene rates, suggests to us, that the rates and style of surface uplift within the forearc of southern Peru has

  9. Rock avalanche occurrence in the San Juan province (Argentina): an analysis of their spatial distribution and main forcing factors (United States)

    Penna, Ivanna; Tonini, Marj; Vega Orozco, Carmen D.; Longchamp, Céline; Derron, Marc-Henri; Jaboyedoff, Michel


    Rock avalanches are frequent phenomena in the Argentinean Andes and a particular high concentration of these events is observed in the Northwest (~25°S) and in the Central Andes from 30°S until the transition with the Patagonian Andes (~38°S). Tectonic deformation and seismicity are generally proposed as main driving factors, with weather and lithologic conditions playing a subordinate role. From 28°S to 33°S, the subhorizontal subduction of the Nazca plate drives higher shortening rates than in the surrounding areas, and an intense seismicity. Main morphotectonic units in this regions are the Cordillera and Precordillera, separated by the Barreal-Calingasta depression. In the southern central part of the flat subduction area (30°30'°-32°30'S), it is observed high valley incision and maximum local relief of 2900 m, while in the Precordillera main fluvial courses developed in the inter-thrust valleys, where local relief is up to 2400 m. In both mountain ranges, we recognized 34 rock avalanches deposits with volumes up to 0.3 km3. There is no apparent lithologic control on detachments, which involved sedimentary, volcanic and granite rocks, even though ~20% of them were favored by layering orientation. However, about 50% of the inventoried rock avalanches with the greatest volumes, developed along tectonic structures or less than 1 km far from them. The main objective of the present study is to explore the spatial distribution of rock avalanche deposits, and compare it with the instrumental seismicity and landscape conditions by means of statistical tools (e.g. exploratory data analyses, Ripley's K-function). Those analyses allow to highlight the spatial correlation between the geological events. Moreover, to visually display the detected cluster spatial patterns we elaborated kernel density maps. Our findings revealed that most of the rock avalanches show a high spatial aggregation mainly between 31°20'S-31°50'S. Main concentration of bedrock landslides

  10. High resolution crustal structure for the region between the Chilenia and Cuyania terrane above the Pampean flat slab of Argentina from local receiver function and petrological analyses (United States)

    Ammirati, J. B.; Alvarado, P. M.; Pérez, S. B.; Beck, S. L.; Porter, R. C.; Zandt, G.


    Jean-Baptiste Ammirati 1,Sofía Perez 1, Patricia Alvarado 1, Susan L. Beck 2, Ryan Porter 3 and George Zandt 2(1) CIGEOBIO-CONICET, Universidad Nacional de San Juan, Argentina (2) The University of Arizona, USA (3) Northern Arizona University, USA At ~31ºS, The subduction of the Nazca plate under the South American plate presents along-strike variations of its dip angle referred to the Chilean-Pampean flat slab. Geological observations suggest that the regional crustal structure is inherited from the accretion of different terranes at Ordovician times and later reactivated during Andean compression since Miocene. Geophysical observations confirmed that the structure is extending in depth with décollement levels that accommodate crustal shortening in the region. In order to get a better insight on the shallow tectonics we computed high frequency local receiver functions from slab seismicity (~100 km depth). Local earthquakes present a higher frequency content that permits a better vertical resolution. Using a common conversion point (CCP) stacking method we obtained cross sections showing high-resolution crustal structure in the western part of the Pampean flat slab region, at the transition between the Precordillera and the Frontal Cordillera. Our results show a well-defined structure and their lateral extent for both units down to 80 km depth. In good agreement with previous studies, our higher resolution images better identify very shallow discontinuities putting more constraints on the relationships with the regional structural geology. Recent petrological analyses combined with RF high-resolution structure also allow us to better understand the regional crustal composition. Interestingly, we are able to observe a shifting structure beneath the Uspallata-Calingasta Valley, highlighting the differences in terms of crustal structure between the Precordillera and the Frontal Cordillera. Previously determined focal mechanisms in the region match well this

  11. Bioleaching of ilmenite and basalt in the presence of iron-oxidizing and iron-scavenging bacteria (United States)

    Navarrete, Jesica U.; Cappelle, Ian J.; Schnittker, Kimberlin; Borrok, David M.


    Bioleaching has been suggested as an alternative to traditional mining techniques in extraterrestrial environments because it does not require extensive infrastructure and bulky hardware. In situ bioleaching of silicate minerals, such as those found on the moon or Mars, has been proposed as a feasible alternative to traditional extraction techniques that require either extreme heat and/or substantial chemical treatment. In this study, we investigated the biotic and abiotic leaching of basaltic rocks (analogues to those found on the moon and Mars) and the mineral ilmenite (FeTiO3) in aqueous environments under acidic (pH ˜ 2.5) and circumneutral pH conditions. The biological leaching experiments were conducted using Acidithiobacillus ferrooxidans, an iron (Fe)-oxidizing bacteria, and Pseudomonas mendocina, an Fe-scavenging bacteria. We found that both strains were able to grow using the Fe(II) derived from the tested basaltic rocks and ilmenite. Although silica leaching rates were the same or slightly less in the bacterial systems with A. ferrooxidans than in the abiotic control systems, the extent of Fe, Al and Ti released (and re-precipitated in new solid phases) was actually greater in the biotic systems. This is likely because the Fe(II) leached from the basalt was immediately oxidized by A. ferrooxidans, and precipitated into Fe(III) phases which causes a change in the equilibrium of the system, i.e. Le Chatelier's principle. Iron(II) in the abiotic experiment was allowed to build up in solution which led to a decrease in its overall release rate. For example, the percentage of Fe, Al and Ti leached (dissolved + reactive mineral precipitates) from the Mars simulant in the A. ferrooxidans experimental system was 34, 41 and 13% of the total Fe, Al and Ti in the basalt, respectively, while the abiotic experimental system released totals of only 11, 25 and 2%. There was, however, no measurable difference in the amounts of Fe and Ti released from ilmenite in the

  12. Bacterial community analysis in chlorpyrifos enrichment cultures via DGGE and use of bacterial consortium for CP biodegradation. (United States)

    Akbar, Shamsa; Sultan, Sikander; Kertesz, Michael


    The organophosphate pesticide chlorpyrifos (CP) has been used extensively since the 1960s for insect control. However, its toxic effects on mammals and persistence in environment necessitate its removal from contaminated sites, biodegradation studies of CP-degrading microbes are therefore of immense importance. Samples from a Pakistani agricultural soil with an extensive history of CP application were used to prepare enrichment cultures using CP as sole carbon source for bacterial community analysis and isolation of CP metabolizing bacteria. Bacterial community analysis (denaturing gradient gel electrophoresis) revealed that the dominant genera enriched under these conditions were Pseudomonas, Acinetobacter and Stenotrophomonas, along with lower numbers of Sphingomonas, Agrobacterium and Burkholderia. Furthermore, it revealed that members of Bacteroidetes, Firmicutes, α- and γ-Proteobacteria and Actinobacteria were present at initial steps of enrichment whereas β-Proteobacteria appeared in later steps and only Proteobacteria were selected by enrichment culturing. However, when CP-degrading strains were isolated from this enrichment culture, the most active organisms were strains of Acinetobacter calcoaceticus, Pseudomonas mendocina and Pseudomonas aeruginosa. These strains degraded 6-7.4 mg L(-1) day(-1) of CP when cultivated in mineral medium, while the consortium of all four strains degraded 9.2 mg L(-1) day(-1) of CP (100 mg L(-1)). Addition of glucose as an additional C source increased the degradation capacity by 8-14 %. After inoculation of contaminated soil with CP (200 mg kg(-1)) disappearance rates were 3.83-4.30 mg kg(-1) day(-1) for individual strains and 4.76 mg kg(-1) day(-1) for the consortium. These results indicate that these organisms are involved in the degradation of CP in soil and represent valuable candidates for in situ bioremediation of contaminated soils and waters.

  13. Aerobic biodegradation of N-nitrosodimethylamine (NDMA) by axenic bacterial strains. (United States)

    Sharp, Jonathan O; Wood, Thomas K; Alvarez-Cohen, Lisa


    The water contaminant N-nitrosodimethylamine (NDMA) is a probable human carcinogen whose appearance in the environment is related to the release of rocket fuel and to chlorine-based disinfection of water and wastewater. Although this compound has been shown to be biodegradable, there is minimal information about the organisms capable of this degradation, and little is understood of the mechanisms or biochemistry involved. This study shows that bacteria expressing monooxygenase enzymes functionally similar to those demonstrated to degrade NDMA in eukaryotes have the capability to degrade NDMA. Specifically, induction of the soluble methane monooxygenase (sMMO) expressed by Methylosinus trichosporium OB3b, the propane monooxygenase (PMO) enzyme of Mycobacterium vaccae JOB-5, and the toluene 4-monooxygenases found in Ralstonia pickettii PKO1 and Pseudomonas mendocina KR1 resulted in NDMA degradation by these strains. In each of these cases, brief exposure to acetylene gas, a suicide substrate for certain monooxygenases, inhibited the degradation of NDMA. Further, Escherichia coli TG1/pBS(Kan) containing recombinant plasmids derived from the toluene monooxygenases found in strains PKO1 and KR1 mimicked the behavior of the parent strains. In contrast, M. trichosporium OB3b expressing the particulate form of MMO, Burkholderia cepacia G4 expressing the toluene 2-monooxygenase, and Pseudomonas putida mt-2 expressing the toluene sidechain monooxygenase were not capable of NDMA degradation. In addition, bacteria expressing aromatic dioxygenases were not capable of NDMA degradation. Finally, Rhodococcus sp. RR1 exhibited the ability to degrade NDMA by an unidentified, constitutively expressed enzyme that, unlike the confirmed monooxygenases, was not inhibited by acetylene exposure. 2005 Wiley Periodicals, Inc.

  14. Bacterial community dynamics during start-up of a trickle-bed bioreactor degrading aromatic compounds. (United States)

    Stoffels, M; Amann, R; Ludwig, W; Hekmat, D; Schleifer, K H


    This study was performed with a laboratory-scale fixed-bed bioreactor degrading a mixture of aromatic compounds (Solvesso100). The starter culture for the bioreactor was prepared in a fermentor with a wastewater sample of a care painting facility as the inoculum and Solvesso100 as the sole carbon source. The bacterial community dynamics in the fermentor and the bioreactor were examined by a conventional isolation procedure and in situ hybridization with fluorescently labeled rRNA-targeted oligonucleotides. Two significant shifts in the bacterial community structure could be demonstrated. The original inoculum from the wastewater of the car factory was rich in proteobacteria of the alpha and beta subclasses, while the final fermentor enrichment was dominated by bacteria closely related to Pseudomonas putida or Pseudomonas mendocina, which both belong to the gamma subclass of the class Proteobacteria. A second significant shift was observed when the fermentor culture was transferred as inoculum to the trickle-bed bioreactor. The community structure in the bioreactor gradually returned to a higher complexity, with the dominance of beta and alpha subclass proteobacteria, whereas the gamma subclass proteobacteria sharply declined. Obviously, the preceded pollutant adaptant did not lead to a significant enrichment of bacteria that finally dominated in the trickle-bed bioreactor. In the course of experiments, three new 16S as well as 23S rRNA-targeted probes for beta subclass proteobacteria were designed, probe SUBU1237 for the genera Burkholderia and Sutterella, probe ALBO34a for the genera Alcaligenes and Bordetella, and probe Bcv13b for Burkholderia cepacia and Burkholderia vietnamiensis. Bacteria hybridizing with the probe Bcv13b represented the main Solvesso100-degrading population in the reactor.

  15. Inhibition of food-related bacteria by antibacterial substances produced by Pseudomonas sp. strains isolated from pasteurized milk

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    Ana Beatriz Ferreira Rangel


    Full Text Available In this work, the production of antimicrobial substances by strains of Pseudomonas sp. isolated from pasteurized milk and their potential action against food-related bacteria were investigated. Samples of pasteurized milk were purchased from arbitrarily chosen commercial establishments in the city of Rio de Janeiro, Brazil. Of the four samples analyzed, three presented several typical colonies of Pseudomonas. About 100 colonies were chosen and subjected to biochemical tests for confirmation of their identity. Eighteen strains of the Pseudomonas genus were identified and submitted to tests for the production of antimicrobial substances. Twelve strains (66.7% were identified as Pseudomonas fluorescens, four (22.2% as P. aeruginosa, one (5.5% as P. mendocina and one (5.5% as P. pseudoalcaligenes. Only two P. fluorescens strains were unable to produce any antimicrobial substance against any of the indicator strains tested. Most of the strains presented a broad spectrum of action, inhibiting reference and food-related strains such as Proteus vulgaris, Proteus mirabilis, Hafnia alvei, Yersinia enterocolitica, Escherichia coli and Salmonella typhi. Five antimicrobial substance-producing strains, which presented the broadest spectrum of action, were also tested against Staphylococcus aureus reference strains and 26 Staphylococcus sp. strains isolated from foods, some of which were resistant to antibiotics. The producer strains 8.1 and 8.3, both P. aeruginosa, were able to inhibit all the staphylococcal strains tested. The antimicrobial substances produced by strains 8.1 and 8.3 did not seem to be typical bacteriocins, since they were resistant to the three proteolytic enzymes tested. Experiments involving the characterization of these substances are being carried out in order to evaluate their biotechnological application.

  16. Essential oils of medicinal plants from the central andes of Argentina: chemical composition, and antifungal, antibacterial, and insect-repellent activities. (United States)

    Lima, Beatriz; López, Sandra; Luna, Lorena; Agüero, María B; Aragón, Liliana; Tapia, Alejandro; Zacchino, Susana; López, María L; Zygadlo, Julio; Feresin, Gabriela E


    The antifungal, antibacterial, and insect-repellent activities of the essential oils (EOs) of Acantholippia seriphioides, Artemisia mendozana, Gymnophyton polycephalum, Satureja parvifolia, Tagetes mendocina, and Lippia integrifolia, collected in the Central Andes area, province of San Juan, Argentina, were investigated. The dermatophytes Microsporum gypseum, Trichophyton mentagrophytes, and T. rubrum were inhibited by the EOs of G. polycephalum, L. integrifolia, and S. parvifolia, with minimum inhibitory concentrations (MICs) between 31.2 and 1000 μg/ml. Moreover, all EOs presented moderate activity against the bacteria tested, and the L. integrifolia and G. polycephalum EOs showed excellent repellent properties against Triatoma infestans, the Chagas disease vector, with repellency values between 60 and 100%. The A. seriphioides, G. polycephalum, and L. integrifolia EOs, obtained by hydrodistillation, were characterized by GC-FID and GC/MS analyses. The highest number of components (40) was identified in L. integrifolia EO, which, along with that of A. seriphioides, contained important amounts of oxygenated monoterpenes (44.35 and 29.72%, resp.). Thymol (27.61%) and carvacrol (13.24%) were the main components of A. seriphioides EO, and borneol, lippifoli-1(6)-en-5-one, and terpinen-4-ol (>8.5%) were the principal compounds of L. integrifolia EO. These results support the idea that oxygenated monoterpenes are the bioactive fractions of the EOs. Finally, the study shows that these Andean species might be used to treat superficial fungal infections and to improve the local Chagas disease situation by vector-control. Copyright © 2011 Verlag Helvetica Chimica Acta AG, Zürich.

  17. C, Sr and Sr isotopic composition on probable vendian- tommotian carbonate sequences in Nw Argentina

    International Nuclear Information System (INIS)

    Sial, A. N.; Ferreira, V.P; Toselli, A.J.; Acenolaza, F.G; Pimentel, M.M; Parada, M.A; Alonso, R.N


    C-isotope stratigraphy is one of the most powerfool tools in Precambrian chronostratigraphy, especially when sediments lack recognizable animal fossils. The δ 13 C secular variation curves for marine carbonates in the Neoproterozoic-Cambrian interval show strong positive-negative excursions, several of them interpreted as the stratigraphic position of ancient ice ages (Hoffman et al. 1998). The Sr isotope composition of the seawater for this age interval is characterized by a continuous increase of 87 Sr/ 86 Sr that is interrupted, several times, by sharp rises, which represent important changes in the Earth history (Montanez et al. 2000). Only limited data on the behavior of C and Sr isotopes in carbonates are available in South America. We examine here carbonate sequences from the Argentine Precordillera, San Juan province, and from other carbonate sequences in NW Argentina that could be, potentially, proxies for the Precambrian-Cambrian transition. We have studied their δ 13 C and 87 Sr/ 86 Sr chemostratigraphy and compare it to global C and Sr isotope secular variation curves for this time span. This study aims to improve the relatively coarse stratigraphic resolution provided only by the study of the fossil record in some of the carbonate successions under consideration (au)

  18. High resolution UHPLC-MS characterization and isolation of main compounds from the antioxidant medicinal plant Parastrephia lucida (Meyen

    Directory of Open Access Journals (Sweden)

    Carlos Echiburu-Chau


    Full Text Available High-resolution mass spectrometry is currently used to determine the mass of biologically active compounds in medicinal plants and food and UHPLC-Orbitrap is a relatively new technology that allows fast fingerprinting and metabolomics analysis. Forty-two metabolites including several phenolic acids, flavonoids, coumarines, tremetones and ent-clerodane diterpenes were accurately identified for the first time in the resin of the medicinal plant Parastrephia lucida (Asteraceae a Chilean native species, commonly called umatola, collected in the pre-cordillera and altiplano regions of northern Chile, by means of UHPLC-PDA-HR-MS. This could be possible by the state of the art technology employed, which allowed well resolved total ion current peaks and the proposal of some biosynthetic relationships between the compounds detected. Some mayor compounds were also isolated using HSCCC. The ethanolic extract showed high total polyphenols content and significant antioxidant capacity. Furthermore, several biological assays were performed that determined the high antioxidant capacity found for the mayor compound isolated from the plant, 11- p-coumaroyloxyltremetone.

  19. A history of Proterozoic terranes in southern South America: From Rodinia to Gondwana

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    C. Casquet


    Full Text Available The role played by Paleoproterozoic cratons in southern South America from the Mesoproterozoic to the Early Cambrian is reconsidered here. This period involved protracted continental amalgamation that led to formation of the supercontinent Rodinia, followed by Neoproterozoic continental break-up, with the consequent opening of Clymene and Iapetus oceans, and finally continental re-assembly as Gondwana through complex oblique collisions in the Late Neoproterozoic to Early Cambrian. The evidence for this is based mainly on a combination of precise U-Pb SHRMP dating and radiogenic isotope data for igneous and metamorphic rocks from a large area extending from the Rio de la Plata craton in the east to the Argentine Precordillera in the west and as far north as Arequipa in Peru. Our interpretation of the paleogeographical and geodynamic evolution invokes a hypothetical Paleoproterozoic block (MARA embracing basement ultimately older than 1.7 Ga in the Western Sierras Pampeanas (Argentina, the Arequipa block (Peru, the Rio Apa block (Brazil, and probably also the Paraguaia block (Bolivia.

  20. Recently active contractile deformation in the forearc of southern Peru (United States)

    Hall, S. R.; Farber, D.; Audin, L.; Finkel, R. C.


    In the Precordillera and Western Cordillera of southern Peru (14°-18°S), vast pediment surfaces have been abandoned through drainage diversion and river incision, with the major drainages carving deep canyons. Within this region, we have identified range-sub-parallel contractile structures that accommodate significant distributed crustal deformation. Young geomorphic features document both the presence and youthfulness of these contractile structures. Here, we determine exposure ages on geomorphic features such as pediment surfaces and fluvial terraces using in situ produced cosmogenic radionuclides, in conjunction with field and remote mapping. This chronologic data reveals that ancient surfaces have been preserved as a result of very low erosion rates. We measure this rate to be chronology and geomorphic mapping, we calculate a Pleistocene river incision rate of ~0.3mm/yr determined from data collected along exoreic rivers. This rate is consistent with longer-term incision rates measured in other localities along this margin. We suggest that, in this region of southern Peru, the steep western wedge of the Andean margin supports the high topography of the Altiplano through a combination of uplift along steeply dipping contractile west-vergent structures and isostatic responses to the focused removal of large amounts of crustal material through canyon incision. Further, that these range sub-parallel structures are related at depth to a thrust system that plays a role in not only the maintenance of the Andean margin, but potentially in its formation as well.

  1. Temporal constraints on the tectonic evolution of Sierra De Famatina, northwestern Argentina, using the fission-track method to date tuffs interbedded in synorogenic clastic sedimentary strata

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    Tabbutt, K.D. (Dartmouth College, Hanover, NH (USA))


    Fission-track dates from seven volcaniclastic units allow time constraints to be placed on synorogenic clastic strata exposed along the flanks of Sierra de Famatina, northwest Argentina. Four formations are exposed along the western margin of Sierra de Famatina. The El Abra conglomerate is composed of clasts eroded from the basement exposed just to the west of Cadena de Paiman. The El Buey Formation contains sediments probably derived from the Precordillera fold and thrust belt to the west. Fission-track dates give a maximum age of 6 Ma for the deposition of both of these formations. The El Durazno Formation, deposited between 6 and 4 Ma, contains proximal volcaniclastic and other clastic rocks derived from the core of Sierra de Famatina. The Santa Florentina conglomerate was derived from the rising Sierra de Famatina and deposited in the past 4 m.y. Sierra de Famatima probably became a positive topographic feature approximately 6 Ma. Prior to that time this region was receiving fine-grained sediments from a distal fold and thrust belt and conglomerates from local basement uplifts. Minor extrusive events (Mogote Formation) coincide both spatially and temporally with deformation along the major reverse faults that control the uplift of Sierra de Famatina. Minimum mean uplift rates calculated for Sierra de Famatina are 0.8 {plus minus} 0.1 mm/yr over a 6.8 m.y. interval.

  2. Grenvillean sutures zones in the northern portion of the Cuyania terrane, Republica Argentina. geophysical evidence

    International Nuclear Information System (INIS)

    Chernicoff, C.; Vujovich, G.


    In the northern portion of the Cuyania terrane there is geophysical evidence for the ocurrence of two ancient WNW suture zones, corresponding to the Guandacol and Vinchina lineaments. The location of these sutures is consistent with analogous structures in Laurentia, in the Ouachita embayment region, where the Grenvillean orogen trends WNW. It is argued that the WNW transform faults pertaining to the Ouachita rift would have developed as a result of a reactivation of compressional structures of identical orientation associated to the accretion of Grenvillean terranes. The Guandacol and Vinchina lineaments would have been in physical continuity with analogous megastructures in the Ouachita embayment region, and they both would have originated as compressional structures, later reactivated as transcurrent fault zones during the late Proterozoic early Paleozoic. The interpretation of the Guandacol and Vinchina lineaments as Grenvillean suture zones would add more complexity to the Cuyania terrane, with respect to what has been described up to now; they could precede the amalgamation of the Pie de Palo and Precordillera terranes (constituents of the Cuyania composite terrane) [es

  3. Structural features of the southern Tulum Fault System, western central Argentina, through gravimetric data and geomorphologic analyses (United States)

    Rodríguez, Aixa I.; Christiansen, Rodolfo O.; Suvires, Graciela M.; Lince Klinger, Federico; Martinez, M. Patricia


    A gravimetric analysis over the Tulum Valley was made. This data was used to reveal the structural setting of the Tulum Fault System situated in the southeastern part of San Juan province in the arid western part of Argentina. This system is the boundary between two geological provinces, the eastern Precordillera Oriental and the Sierras Pampeanas Occidentales. Gravity data was processed using upward continuation and vertical derivative filters and all the results were compared with the geomorphological and the drainage systems maps of the area. Our assessment confirms the presence of two structures in the Pampeano basement with positive anomalies similar to those found in Valdivia and Barboza hills, two important depocenters with low gravimetric gradients separated by a zone with higher gravity anomalies than the depocenters to the east and west. In view of this, a structural map is proposed for the area. This system is important not only because it is the boundary between two geological provinces and has significance regarding regional tectonic issues but also because it controls the surface drainage, soils distribution and groundwater flow of the Tulum basin conditioning the land use distribution.

  4. Stratigraphical distribution of the Ordovician conodont Erraticodon Dzik in Argentina (United States)

    Heredia, S.; Carlorosi, J.; Mestre, A.; Soria, T.


    Three different species of the Ordovician genus Erraticodon Dzik are described and illustrated. Erraticodon patu Cooper is reported from the Lower-Midde Ordovician strata of the Acoite and Alto del Cóndor formations. E. cf. Erraticodon balticus and Erraticodon hexianensis from Middle Ordovician carbonate deposits of the San Juan Formation are analyzed and compared to specimens of these species from Australia, China, Newfoundland, and Baltica. E. patu and E. hexianensis are recorded for first time in the San Juan Formation of Precordillera. The elements of E. cf. E. balticus resemble closely E. balticus Dzik but lack the important denticle on the posterior process of the S elements. An evaluation of the stratigraphic occurrences of these species relative to those of key Lower and Middle Ordovician conodont species such as Trapezognathus diprion Lindström, Oepikodus intermedius Serpagli, Baltoniodus triangularis (Lindström), Baltoniodus navis Lindström, Yangtzeplacognathus crassus (Chen and Zhang) and Eoplacognathus pseudoplanus (Viira) indicates they value for biostratigraphic correlation.

  5. Integrated U-Pb zircon and palynological/palaeofloristic age determinations of a Bashkirian palaeofjord fill, Quebrada Grande (Western Argentina) (United States)

    Valdez Buso, Victoria; di Pasquo, Mercedes; Milana, Juan Pablo; Kneller, Benjamin; Fallgatter, Claus; Junior, Farid Chemale; Gomes Paim, Paulo Sérgio


    This work presents a new age framework for the main Bashkirian glacio-eustatic transgression in Argentina, including the first absolute age for the Jejenes Formation, San Juan Province, based on radiometric dating of a crystal-rich tuff, supported by palynological and palaeofloristic studies, and presented within a revised palaeogeographic setting. The Jejenes Formation represents the glacial to postglacial fill of the Quebrada Grande palaeofjord carved in the Eastern Precordillera. The succession has been subdivided into five stages, the youngest of which suggests a previously unrecognised glacial event for this locality. Six productive levels for palynology were found within proglacial strata, and in the base and top of the succeeding interglacial stage. Palynoassemblages are characterized by poorly preserved trilete spores and monosaccate pollen grains along with a large amount of terrestrial phytoclasts. Main species indicating the Raistrickia densa-Convolutispora muriornata SubZone (DMa SZ) are Vallatisporites ciliaris, Cristatisporites rollerii, C. stellatus, C. chacoparanensis, C. inconstans and monosaccates such as Circumplicatipollis plicatus. This DMa SZ is estimated as Serpukhovian/Bashkirian and characterizes the glacial-related Guandacol Formation and equivalents units of the western Paganzo Basin. A tuffaceous level in the proglacial unit, bearing platyspermic seeds, plant remains and palynomorphs, yielded first-cycle volcanic zircons that were analysed by SHRIMP. An absolute age of 321.3 ± 5.3 Ma confirms a Bashkirian age for the main postglacial transgression in the Paganzo Basin, and offers a novel calibration for the palynoassemblages of DMa SZ that occurs elsewhere in Western Argentina.

  6. The metamorphic basement of the Cordillera Frontal of Mendoza: New geochronologic and isotopic data

    International Nuclear Information System (INIS)

    Basei, Miguel; Ramos, Victor A.; Vujovich, Graciela I.; Poma, Stella


    The metamorphic rocks of the Cordillera Frontal exposed in the Cordon del Portillo, Mendoza were examined by Rb/Sr geochronology and Nd/Sm isotopic analysis. The Rb/Sr data defined a Devonian age for the last metamorphic episode, similar to the previous K/Ar and Ar/Ar ages obtained in this region and western Precordillera. The isotopic analysis identified three sets of model ages: 1.- The oldest corresponds to a set of meta sedimentary rocks with a model age of 1,400 to 1,700 Ma; 2.- A monzogranodiorite with a model age of 1,000 Ma; and 3.- Metabasites with model ages between 577 and 330 Ma. These rocks are interpreted as 1.- A typical Grenvillian derived basement; 2.- Late Paleozoic granitoids derived from a different Proterozoic basement; and 3.- Some Eopaleozoic metabasites tectonically inter fingered with the Grenvillian basement. These new data are coherent with the existence of a Laurentia derived terrane, Chilenia, that was separated by oceanic rocks from the basement of Pre cordillera during Eopaleozoic times. This last basement known as the Cuyania terrane, was also derived from Laurentia. (author)

  7. A Comparative Analysis of Seismological and Gravimetric Crustal Thicknesses below the Andean Region with Flat Subduction of the Nazca Plate

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    Mario E. Gimenez


    Full Text Available A gravimetric study was carried out in a region of the Central Andean Range between 28∘ and 32∘ south latitudes and from 72∘ and 66∘ west longitudes. The seismological and gravimetrical Moho models were compared in a sector which coincides with the seismological stations of the CHARGE project. The comparison reveals discrepancies between the gravity Moho depths and those obtained from seismological investigations (CHARGE project, the latter giving deeper values than those resulting from the gravimetric inversion. These discrepancies are attenuated when the positive gravimetric effect of the Nazca plate is considered. Nonetheless, a small residuum of about 5 km remains beneath the Cuyania terrane region, to the east of the main Andean chain. This residuum could be gravimetrically justified if the existence of a high density or eclogitized portion of the lower crust is considered. This result differed from the interpretations from Project “CHARGE” which revealed that the entire inferior crust extending from the Precordillera to the occidental “Sierras Pampeanas” could be “eclogitized”. In this same sector, we calculated the effective elastic thickness (Te of the crust. These results indicated an anomalous value of Te = 30 km below the Cuyania terrane. This is further conclusive evidence of the fact that the Cuyania terrane is allochthonous, for which also geological evidences exist.

  8. Three-dimensional models of P wave velocity and P-to-S velocity ratio in the southern central Andes by simultaneous inversion of local earthquake data (United States)

    Graeber, Frank M.; Asch, Günter


    The PISCO'94 (Proyecto de Investigatión Sismológica de la Cordillera Occidental, 1994) seismological network of 31 digital broad band and short-period three-component seismometers was deployed in northern Chile between the Coastal Cordillera and the Western Cordillera. More than 5300 local seismic events were observed in a 100 day period. A subset of high-quality P and S arrival time data was used to invert simultaneously for hypocenters and velocity structure. Additional data from two other networks in the region could be included. The velocity models show a number of prominent anomalies, outlining an extremely thickened crust (about 70 km) beneath the forearc region, an anomalous crustal structure beneath the recent magmatic arc (Western Cordillera) characterized by very low velocities, and a high-velocity slab. A region of an increased Vp/Vs ratio has been found directly above the Wadati-Benioff zone, which might be caused by hydration processes. A zone of lower than average velocities and a high Vp/Vs ratio might correspond to the asthenospheric wedge. The upper edge of the Wadati-Benioff zone is sharply defined by intermediate depth hypocenters, while evidence for a double seismic zone can hardly be seen. Crustal events between the Precordillera and the Western Cordillera have been observed for the first time and are mainly located in the vicinity of the Salar de Atacama down to depths of about 40 km.

  9. La morphogenèse des plaines et des collines du secteur occidental de l'Equateur

    Directory of Open Access Journals (Sweden)


    Full Text Available Les régions occidentales équatoriennes appartiennent au grand bourrelet des cordillères andines dont elles constituent une avant fosse et une précordillère côtière. L'évolution commence dès la mise en place des grands ensembles structuraux andins et elle est caractérisée par la migration d'Ouest en Est de l'axe de la fosse de subsidence. Le remblaiement par les formations volcaniques et sédimentaires et les mouvements tectoniques qui se sont succédés depuis le Crétacé ont vu la mise en place d'une cordillère littorale ou une tectonique cassante sur un matériel très différencié a créé une série de plateaux et de fossés encadrant une ligne de crête d'allure lourde et massive. Au pied des Andes, la fosse est remblayée au Nord, émergée et découpée en plateaux substructuraux tandis qu'au centre le colmatage est très imparfait dans un secteur qui parait encore en légère subsidence et que le Sud reste toujours ennoyé et constitue le Golfe de Guayaquil. Las regiones occidentales ecuatorianas pertenecen al gran burlete de las cordilleras andinas en las que constituyen una antefosa y una precordillera costeña. La evolución comienza desde su emplazamiento en los grandes conjuntos estructurales andinos y está caracterizada por la migración de Oeste al Este del eje de la fosa de subsidencia. El terraplenado por las formaciones volcánicas y sedimentarias y los movimientos tectónicos que se han sucedido desde el cretáceo han visto el emplazamiento de una cordillera litoral donde una tectónica quebradiza sobre un material muy diferenciado ha creado una serie de mesetas y de fosas enmarcando una línea de cresta de aspecto pesado y macizo. Al pie de los Andes, la fosa está terraplenada al Norte, emergida y recortada en mesetas subestructurales mientras que en el centro el colmataje es muy imperfecto en un sector que aparece aún en ligera subsidencia y que el sur permanece siempre anegado y constituye el Golfo de

  10. The Amazon-Laurentian connection as viewed from the Middle Proterozoic rocks in the central Andes, western Bolivia and northern Chile (United States)

    Tosdal, R.M.


    between these cratons and seemingly precluding part of the Arequipa-Antofalla craton from being a detached fragment of another craton such as eastern Laurentia, which has been characterized by a different U/Pb history. Pb isotopic compositions for the Arequipa-Antofalla craton are, furthermore, distinct from those of the Proterozoic basement in the Precordillera terrane, western Argentina, indicating a Pb isotopic and presumably a tectonic boundary between them. The Pb isotopic compositions for the Precordillera basement are similar to those of eastern Laurentia, and support other data indicating that these rocks are a detached fragment of North America. Finally, the distinct Pb isotopic evolution history of the Arequipa-Antofalla craton and eastern Laurentia require minor modification to tectonic models linking eastern North America-Scotland to the oroclinal bend in western South America.

  11. Pyoverdine synthesis by the Mn(II-oxidizing bacterium Pseudomonas putida GB-1

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    Dorothy Lundquist Parker


    Full Text Available When iron-starved, the Mn(II-oxidizing bacteria Pseudomonas putida strains GB-1 and MnB1 produce pyoverdines (PVDGB-1 and PVDMnB1, siderophores that both influence iron uptake and inhibit manganese(II oxidation by these strains. To explore the properties and genetics of a PVD that can affect manganese oxidation, LC-MS/MS and various siderotyping techniques were used to identify the peptides of PVDGB-1 and PVDMnB1 as being (for both PVDs: chromophore-Asp-Lys-OHAsp-Ser-Gly-aThr-Lys-cOHOrn, resembling a structure previously reported for P. putida CFML 90-51, which does not oxidize Mn. All three strains also produced an azotobactin and a sulfonated PVD, each with the peptide sequence above, but with unknown regulatory or metabolic effects. Bioinformatic analysis of the sequenced genome of P. putida GB-1 suggested that a particular non-ribosomal peptide synthetase, coded by the operon PputGB1_4083-4086, could produce the peptide backbone of PVDGB-1. To verify this prediction, plasmid integration disruption of PputGB1_4083 was performed and the resulting mutant failed to produce detectable PVD. In silico analysis of the modules in PputGB1_4083-4086 predicted a peptide sequence of Asp-Lys-Asp-Ser-Ala-Thr-Lsy-Orn, which closely matches the peptide determined by MS/MS. To extend these studies to other organisms, various Mn(II-oxidizing and non-oxidizing isolates of P. putida, P. fluorescens, P. marincola, P. fluorescens-syringae group, P. mendocina-resinovorans group and P. stutzerii group were screened for PVD synthesis. The PVD producers (12 out of 16 tested strains were siderotyped and placed into four sets of differing PVD structures, some corresponding to previously characterized PVDs and some to novel PVDs. These results combined with previous studies suggested that the presence of OHAsp or the flexibility of the pyoverdine polypeptide may enable efficient binding of Mn(III.

  12. Pyoverdine synthesis by the Mn(II)-oxidizing bacterium Pseudomonas putida GB-1 (United States)

    Parker, Dorothy L.; Lee, Sung-Woo; Geszvain, Kati; Davis, Richard E.; Gruffaz, Christelle; Meyer, Jean-Marie; Torpey, Justin W.; Tebo, Bradley M.


    When iron-starved, the Mn(II)-oxidizing bacteria Pseudomonas putida strains GB-1 and MnB1 produce pyoverdines (PVDGB-1 and PVDMnB1), siderophores that both influence iron uptake and inhibit manganese(II) oxidation by these strains. To explore the properties and genetics of a PVD that can affect manganese oxidation, LC-MS/MS, and various siderotyping techniques were used to identify the peptides of PVDGB-1 and PVDMnB1 as being (for both PVDs): chromophore-Asp-Lys-OHAsp-Ser-Gly-aThr-Lys-cOHOrn, resembling a structure previously reported for P. putida CFML 90-51, which does not oxidize Mn. All three strains also produced an azotobactin and a sulfonated PVD, each with the peptide sequence above, but with unknown regulatory or metabolic effects. Bioinformatic analysis of the sequenced genome of P. putida GB-1 suggested that a particular non-ribosomal peptide synthetase (NRPS), coded by the operon PputGB1_4083-4086, could produce the peptide backbone of PVDGB-1. To verify this prediction, plasmid integration disruption of PputGB1_4083 was performed and the resulting mutant failed to produce detectable PVD. In silico analysis of the modules in PputGB1_4083-4086 predicted a peptide sequence of Asp-Lys-Asp-Ser-Ala-Thr-Lsy-Orn, which closely matches the peptide determined by MS/MS. To extend these studies to other organisms, various Mn(II)-oxidizing and non-oxidizing isolates of P. putida, P. fluorescens, P. marincola, P. fluorescens-syringae group, P. mendocina-resinovorans group, and P. stutzerii group were screened for PVD synthesis. The PVD producers (12 out of 16 tested strains) were siderotyped and placed into four sets of differing PVD structures, some corresponding to previously characterized PVDs and some to novel PVDs. These results combined with previous studies suggested that the presence of OHAsp or the flexibility of the pyoverdine polypeptide may enable efficient binding of Mn(III). PMID:24847318

  13. Hydrogeology and sustainable future groundwater abstraction from the Agua Verde aquifer in the Atacama Desert, northern Chile (United States)

    Urrutia, Javier; Jódar, Jorge; Medina, Agustín; Herrera, Christian; Chong, Guillermo; Urqueta, Harry; Luque, José A.


    The hyper-arid conditions prevailing in Agua Verde aquifer in northern Chile make this system the most important water source for nearby towns and mining industries. Due to the growing demand for water in this region, recharge is investigated along with the impact of intense pumping activity in this aquifer. A conceptual model of the hydrogeological system is developed and implemented into a two-dimensional groundwater-flow numerical model. To assess the impact of climate change and groundwater extraction, several scenarios are simulated considering variations in both aquifer recharge and withdrawals. The estimated average groundwater lateral recharge from Precordillera (pre-mountain range) is about 4,482 m3/day. The scenarios that consider an increase of water withdrawal show a non-sustainable groundwater consumption leading to an over-exploitation of the resource, because the outflows surpasses inflows, causing storage depletion. The greater the depletion, the larger the impact of recharge reduction caused by the considered future climate change. This result indicates that the combined effects of such factors may have a severe impact on groundwater availability as found in other groundwater-dependent regions located in arid environments. Furthermore, the scenarios that consider a reduction of the extraction flow rate show that it may be possible to partially alleviate the damage already caused to the aquifer by the continuous extractions since 1974, and it can partially counteract climate change impacts on future groundwater availability caused by a decrease in precipitation (and so in recharge), if the desalination plant in Taltal increases its capacity.

  14. 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) (United States)

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


    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.

  15. A Cambrian mixed carbonate-siliciclastic platform in SW Gondwana: evidence from the Western Sierras Pampeanas (Argentina) and implications for the early Paleozoic paleogeography of the proto-Andean margin (United States)

    Ramacciotti, Carlos D.; Casquet, César; Baldo, Edgardo G.; Galindo, Carmen; Pankhurst, Robert J.; Verdecchia, Sebastián O.; Rapela, Carlos W.; Fanning, Mark


    The Western Sierras Pampeanas (WSP) of Argentina record a protracted geological history from the Mesoproterozoic assembly of the Rodinia supercontinent to the early Paleozoic tectonic evolution of SW Gondwana. Two well-known orogenies took place at the proto-Andean margin of Gondwana in the Cambrian and the Ordovician, i.e., the Pampean (545-520 Ma) and Famatinian (490-440 Ma) orogenies, respectively. Between them, an extensive continental platform was developed, where mixed carbonate-siliciclastic sedimentation occurred. This platform was later involved in the Famatinian orogeny when it underwent penetrative deformation and metamorphism. The platform apparently extended from Patagonia to northwestern Argentina and the Eastern Sierras Pampeanas, and has probable equivalents in SW Africa, Peru, and Bolivia. The WSP record the outer (deepest) part of the platform, where carbonates were deposited in addition to siliciclastic sediments. Detrital zircon U-Pb SHRIMP ages from clastic metasedimentary successions and Sr-isotope compositions of marbles from the WSP suggest depositional ages between ca. 525 and 490 Ma. The detrital zircon age patterns further suggest that clastic sedimentation took place in two stages. The first was sourced mainly from re-working of the underlying Neoproterozoic metasedimentary rocks and the uplifted core of the early Cambrian Pampean orogen, without input from the Paleoproterozoic Río de la Plata craton. Sediments of the second stage resulted from the erosion of the still emerged Pampean belt and the Neoproterozoic Brasiliano orogen in the NE with some contribution from the Río de la Plata craton. An important conclusion is that the WSP basement was already part of SW Gondwana in the early Cambrian, and not part of the exotic Precordillera/Cuyania terrane, as was previously thought.

  16. Joint TEM and MT aquifer study in the Atacama Desert, North Chile (United States)

    Ruthsatz, Alexander D.; Sarmiento Flores, Alvaro; Diaz, Daniel; Reinoso, Pablo Salazar; Herrera, Cristian; Brasse, Heinrich


    The Atacama Desert represents one of the driest regions on earth, and despite the absence of sustainable clean water reserves the demand has increased drastically since 1970 as a result of growing population and expanding mining activities. Magnetotelluric (MT) and Transient Electromagnetic (TEM) measurements were carried out for groundwater exploration in late 2015 in the area of the Profeta Basin at the western margin of the Chilean Precordillera. Both methods complement each other: While MT in general attains larger penetration depths, TEM allows better resolution of near surface layers; furthermore TEM is free from galvanic distortion. Data were collected along three profiles, enabling a continuous resistivity image from the surface to at least several hundred meters depth. TEM data were inverted in a 1-D manner, consistently yielding a poorly conductive near-surface layer with a thickness of approximately 30 m and below a well-conducting layer which we interpret as the aquifer with resistivities around 10 Ωm. At marginal sites of the main SW-NE-profile the resistive basement was found in 150 m. These depths are confirmed by interpretation of the MT soundings. Those were firstly inverted with a 2-D approach and then by 3-D inversion as clear indications of three-dimensionality exist. Several modeling runs were performed with different combinations of transfer functions and smoothing parameters. Generally, MT and TEM results agree reasonably well and an overall image of the resistivity structures in the Profeta Basin could be achieved. The aquifer reaches depths of more than 500 m in parts and, by applying Archie's law, resistivities of 1 Ωm can be assumed, indicating highly saline fluids from the source region of the surrounding high Andes under persisting arid conditions.

  17. Geology and geochemistry of the Atacama Desert. (United States)

    Tapia, J; González, R; Townley, B; Oliveros, V; Álvarez, F; Aguilar, G; Menzies, A; Calderón, M


    The Atacama Desert, the driest of its kind on Earth, hosts a number of unique geological and geochemical features that make it unlike any other environment on the planet. Considering its location on the western border of South America, between 17 and 28 °S, its climate has been characterized as arid to hyperarid for at least the past 10 million years. Notably dry climatic conditions of the Atacama Desert have been related to uplift of the Andes and are believed to have played an important role in the development of the most distinctive features of this desert, including: (i) nitrates and iodine deposits in the Central Depression, (ii) secondary enrichment in porphyry copper deposits in the Precordillera, (iii) Li enrichment in salt flats of the Altiplano, and (iv) life in extreme habitats. The geology and physiography of the Atacama Desert have been largely shaped by the convergent margin present since the Mesozoic era. The geochemistry of surface materials is related to rock geochemistry (Co, Cr, Fe, Mn, V, and Zn), salt flats, and evaporite compositions in endorheic basins (As, B, and Li), in addition to anthropogenic activities (Cu, Mo, and Pb). The composition of surface water is highly variable, nonetheless in general it presents a circumneutral pH with higher conductivity and total dissolved solids in brines. Major water constituents, with the exception of HCO 3 - , are generally related to the increase of salinity, and despite the fact that trace elements are not well-documented, surface waters of the Atacama Desert are enriched in As, B, and Li when compared to the average respective concentrations in rivers worldwide.

  18. Active deformation in the northern Sierra de Valle Fértil, Sierras Pampeanas, Argentina (United States)

    Ortiz, Gustavo; Alvarado, Patricia; Fosdick, Julie C.; Perucca, Laura; Saez, Mauro; Venerdini, Agostina


    The Western Sierras Pampeanas region in the San Juan Province is characterized by thick-skinned deformation with approximately N-S trending ranges of average heights of 2500 m and a high frequency occurrence of seismic activity. Its location to the east of the mainly thin-skinned tectonics of the Argentine Precordillera fold-and-thrust belt suggests that at 30°S, deformation is concentrated in a narrow zone involving these two morphostructural units. In this paper, we present new apatite (U-Th)/He results (AHe) across the northern part of the Sierra de Valle Fértil (around 30°S) and analyze them in a framework of thermochronologic available datasets. We found Pliocene AHe results for Carboniferous and Triassic strata in the northern Sierra de Valle Fértil consistent with the hypothesis of recent cooling and inferred erosional denudation concentrated along the northern end of this mountain range. Our analysis shows that this northern region may have evolved under different conditions than the central part of the Sierra de Valle Fértil. Previous studies have observed AHe ages consistent with Permian through Cretaceous cooling, indicating the middle part of the Sierra de Valle Fértil remained near surface before the Pampean slab subduction flattening process. Those studies also obtained ˜5 My cooling ages in the southern part of the Sierra de Valle Fértil, which are similar to our results in the northern end of the range. Taken together, these results suggest a pattern of young deformation in the northern and southern low elevation ends of the Sierra de Valle Fértil consistent with regions of high seismic activity, and Quaternary active faulting along the western-bounding thrust fault of the Sierra de Valle Fértil.

  19. Characterization of landslide dams in the San Juan province (Argentina) (United States)

    Penna, Ivanna; Longchamp, Celine; Derron, Marc-Henri; Jaboyedoff, Michel


    River blockages caused by landslide deposition are common phenomena in active mountain chains, influencing erosion-sedimentation patterns and acting as primary and secondary hazards. Regional scale analyses regarding their spatial distribution and morphometry allow establishing boundary conditions for their occurrence and stability, and determine differences among regions with different landscape and climatic conditions. Owing to the combination of endogenous and exogenous factors, landslide dams are frequent phenomena in the Andes. In the Argentinean NW and the Patagonian Andes, previous studies showed that stability of landslide dams determined by morphometric parameters generally matched satisfactorily with dam behavior, with some exceptions in which climatic component played an important role in dam longevity. Aiming to expand the knowledge of landslide dams in the Argentinean Andes, in this work we analyzed the stability of rock avalanche dams in the Pampeam flat slab subduction zone. In the study area, mountain dynamics creates suitable conditions for the occurrence of 34 rock avalanches with volumes up to 0.3 km3. They developed in deeply carved valleys (Cordillera) and Inter-thrust valleys (Precordillera). 22 impoundments of rivers resulted from channelized rock avalanches with long runouts (4-10 km) that blocked tributaries rivers, but most of them by rock avalanches that filled the valley bottom, with run up in the opposite slope and limited movement parallel to the valley axis. Most of the dams breached in unknown times, except for the last event that occurred on November 12th 2005. The quantification of morphometric parameters and contributing areas indicates the existence of dams with dimensionless blockage index above 2.75 (stable domain) and below 3.08 (instable domain). The Los Erizos dam in our study area and the Barrancas dam in the Patagonian Andes show that besides morphometric parameters, climatic conditions are decisive. Stable landslide dams

  20. Upper Carboniferous retroarc volcanism with submarine and subaerial facies at the western Gondwana margin of Argentina (United States)

    Koukharsky, M.; Kleiman, L.; Etcheverría, M.; Quenardelle, S.; Bercowski, F.


    During Late Carboniferous times a continental magmatic arc developed at the western margin of Gondwana in South America, as several marine sedimentary basins were formed at the same time in the retroarc region. North of 33°S, at Cordón Agua del Jagüel, Precordillera of Mendoza, Argentina, a volcanic sequence crops out which was emplaced in a submarine environment with some subaerial exposures, and it is intercalated in marine sediments of Agua del Jagüel Formation, which fills of one of these retroarc basins. This paper presents, for the first time, a facies analyses together with geochemical and isotopic data of this volcanic suite, suggesting its deposition in an ensialic retroarc marine basin. The volcanic succession comprises debris flows with either sedimentary or volcanic fragments, base surge, resedimented massive and laminated dacitic-andesitic hyaloclastite, pillow lava, basic hyaloclastite and dacitic-andesitic lavas and hyaloclastite facies. Its composition is bimodal, either basaltic or dacitic-andesitic. The geochemistry data indicate a subalkaline, low K calk-alkaline and metaluminous affinity. The geochemistry of the basalts points to an origin of the magmas from a depleted mantle source with some crustal contamination. Conversely, the geochemistry of the dacites-andesites shows an important participation of both crustal components and subduction related fluids. A different magmatic source for the basalts than for the dacites-andesites is also supported by Sr and Nd isotopic initial ratios and Nd model ages. The characteristics of this magmatic suite suggest its emplacement in an extensional setting probably associated with the presence of a steepened subduction zone at this latitude during Upper Carboniferous times.

  1. Age and origin of coeval TTG, I- and S-type granites in the Famatinian belt of NW Argentina

    International Nuclear Information System (INIS)

    Rapela, C.W.


    Full text: Located on the Palaeozoic Pacific margin of Gondwana, at the opposite extreme to the Lachlan Fold Belt, the Sierras Pampeanas of central and NW Argentina also constitute a large granitic province displaying the coeval concurrence of I and S-type magmas. The Famatinian magmatic belt consists mostly of granitoids emplaced in Early Ordovician times, after Cambrian accretion of the Pampean terrane and before the Late Ordovician/Silurian accretion of the Precordillera terrane. New SHRIMP U-Pb zircon ages, isotope and geochemical data are used to interpret the petrogenesis of this belt. Three types of granitoid are recognized in the Famatinian belt, based on lithology and geochemical data. These are (a) a minor trondhjemite-tonalite-granodiorite (TTG) group, which occurs only in the Pampean foreland, (b) a metaluminous I-type gabbromonzogranite suite, and (c) S-type granites, which occur both as small cordieritic intrusions associated with l-type granodiorites and as large batholithic masses. Twelve new SHRIMP U-Pb zircon ages establish the contemporaneity of all three types in Early Ordovician times (mainly 470-490 Ma ago). Sr- and Nd-isotopic data suggest that, apart from some TTG plutons with asthenospheric characteristics, the remaining magmas were derived from a Proterozoic crust-lithospheric mantle section (Nd model ages of 1500-1700 Ma). Granulite xenoliths in Cretaceous alkalic rocks that have been described by other authors may represent samples of this source region. Trace element modelling suggests that the TTG and I-type gabbros originated by variable melting of a lithospheric gabbroid source at 10-12 kbar and ca. 5 kbar, respectively. The voluminous intermediate and acidic I-types, which show a trend to slightly more evolved isotopic signatures than the inferred source, probably represent hybridization of the most primitive magmas with lower and middle crustal melts. The highly peraluminous S-type granites have similar isotopic and inherited

  2. Active basement uplift as seen with cosmogenic lenses: the Sierra Pie de Palo case (Western Argentina) (United States)

    Siame, L. L.; Sébrier, M.; Costa, C. H.; Ahumada, E. A.; Bellier, O.


    The Andean foreland of western Argentina (28°S-33°S) corresponds to retroarc deformations associated with the ongoing flat subduction of the Nazca plate beneath the South American lithosphere, and associated with high levels of seismic activity and crustal active faulting. To improve earthquake source identification and characterization in the San Juan region, data from seismology, structural geology and quantitative geomorphology can be integrated and combined to provide a seismotectonic model. In this model, the Andean back-arc of western Argentina has to be regarded as an obliquely converging foreland where Plio-Quaternary deformations are partitioned between strike-slip and thrust motions that are localized on the E-verging, thin-skinned Argentine Precordillera, and the W-verging thick-skinned Sierras Pampeanas, respectively. In this domain, the Sierra Pie de Palo is a key structure playing a major role in the partitioning of the Plio-Quaternary deformations. Located in the westernmost Sierras Pampeanas, the Sierra Pie de Palo forms a NNE striking, 80 km-long and 35-40 km-wide, ellipsoid range that reaches elevation as high as 3162 m. This mountain range is an actively growing basement fold associated with a high level of seismic activity (e.g., the November 23, 1977, Caucete, Mw 7.4 earthquake). To evaluate the degree of tectonic activity around the Sierra Pie de Palo, we combined a detailed morphometric analysis of the topography together with in situ-produced cosmogenic 10Be concentrations measured in (1) bedrock outcrops corresponding to the exhumed erosional regional surface, (2) surface boulders abandoned on alluvial fans deformed by active faults, and (3) in fluvial sediments sampled at the outlets of selected watersheds that drains out from the Sierra Pie de Palo. All together, our results allows: (1) assessing quantitative constraints on the rate of tectonic and denudation processes that are responsible for the active growth and erosion of the Sierra

  3. New glacial evidences at the Talacasto paleofjord (Paganzo basin, W-Argentina) and its implications for the paleogeography of the Gondwana margin (United States)

    Aquino, Carolina Danielski; Milana, Juan Pablo; Faccini, Ubiratan Ferrucio


    The Talacasto paleovalley is situated in the Central Precordillera of San Juan, Argentina, where upper Carboniferous-Permian rocks (Paganzo Group) rest on Devonian sandstones of the Punta Negra Formation. This outcrop is an excellent example of a glacial valley-fill sequence that records at least two high-frequency cycles of the advance and retreat of a glacier into the valley. The paleocurrent analysis shows transport predominantly to the south, indicating that at this site the ice flow differs from the other nearby paleovalleys. Evidence of the glacial origin of this valley can be seen in the glacial striae on the valley's sides, as well as the U-shape of the valley, indicated by very steep locally overhanging valley walls. Deglaciation is indicated by a set of retransported conglomerates deposited in a shallow-water environment followed by a transgressive succession, which suggests eustatic rise due to meltwater input to the paleofjord. The complete sedimentary succession records distinct stages in the evolution of the valley-fill, represented by seven stratigraphical units. These units are identified based on facies associations and their interpreted depositional setting. Units 1 to 5 show one cycle of deglaciation and unit 6 marks the beginning of a new cycle of glacier advance which is characterized by different types of glacial deposits. All units show evidence of glacial influence such as dropstones and striated clasts, which indicates that the glaciers were always present in the valley or in adjacent areas during sedimentation. The Talacasto paleofjord provides good evidence of the Late Paleozoic Gondwana glaciation in western Argentina and examples of sedimentary successions which have been interpreted as being deposited by a confined wet-based glacier in advance and retreat cycles, with eventual release of icebergs into the basin. The outcrop is also a key for reconstructing the local glacial paleogeography, and it suggests a new interpretation that is

  4. Structural and numerical modeling of fluid flow and evolving stress fields at a transtensional stepover: A Miocene Andean porphyry copper system as a case study. (United States)

    Nuñez, R. C.; Griffith, W. A.; Mitchell, T. M.; Marquardt, C.; Iturrieta, P. C.; Cembrano, J. M.


    Obliquely convergent subduction orogens show both margin-parallel and margin-oblique fault systems that are spatially and temporally associated with ore deposits and geothermal systems within the volcanic arc. Fault orientation and mechanical interaction among different fault systems influence the stress field in these arrangements, thus playing a first order control on the regional to local-scale fluid migration paths as documented by the spatial distribution of fault-vein arrays. Our selected case study is a Miocene porphyry copper-type system that crops out in the precordillera of the Maule region along the Teno river Valley (ca. 35°S). Several regional to local faults were recognized in the field: (1) Two first-order, N-striking subvertical dextral faults overlapping at a right stepover; (2) Second-order, N60°E-striking steeply-dipping, dextral-normal faults located at the stepover, and (3) N40°-60°W striking subvertical, sinistral faults crossing the stepover zone. The regional and local scale geology is characterized by volcano-sedimentary rocks (Upper Eocene- Lower Miocene), intruded by Miocene granodioritic plutons (U-Pb zircon age of 18.2 ± 0.11 Ma) and coeval dikes. We implement a 2D boundary element displacement discontinuity method (BEM) model to test the mechanical feasibility of kinematic model of the structural development of the porphyry copper-type system in the stepover between N-striking faults. The model yields the stress field within the stepover region and shows slip and potential opening distribution along the N-striking master faults under a regionally imposed stress field. The model shows that σ1 rotates clockwise where the main faults approach each other, becoming EW when they overlap. This, in turn leads to the generation of both NE- and NW-striking faults within the stepover area. Model results are consistent with the structural and kinematic data collected in the field attesting for enhanced permeability and fluid flow transport

  5. Mutación fundadora en una familia argentina con cáncer colorrectal hereditario Detection of a founder mutation in an Argentine family with hereditary non polyposis colorectal cancer

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    Laura Gómez


    Full Text Available El cáncer colorrectal hereditario no poliposo (CCHNP se relaciona con mutaciones en los genes reparadores de ADN (MLH1, MSH2 y MSH6. La mayoría de estas alteraciones son familia-específicas y su detección suele requerir la secuenciación completa de los genes relacionados. Se detectó una mutación puntual (2269-2270insT en el último codón del gen MLH1 en familias de un área del norte de Italia (Reggio Emilia y su origen se considera debido a un efecto fundador. En este trabajo presentamos una familia mendocina con CCHNP portadora de la misma mutación, cuyos ancestros eran oriundos de Reggio Emilia. Para la detección de la mutación se diseñó una estrategia basada en PCR y posterior corte enzimático. La mutación fue hallada en tres integrantes de la familia estudiada, dos de los cuales no presentaban sintomatología clínica. Estos pacientes fueron seguidos preventivamente mediante colonoscopias. La metodología utilizada en nuestro laboratorio fue específica y sensible para la detección de una mutación previamente registrada y permitió realizar el diagnóstico genético molecular en el país, evitando el envío de muestras al extranjero. Es de importancia destacar que el diagnóstico genético pre-sintomático de cáncer hereditario, enfocado desde un grupo multidisciplinario de profesionales, permite un mejor seguimiento y apoyo a las familias afectadas.Hereditary non polyposis colorectal cancer (HNPCC has been related to mutations in the DNA mismatch repair genes (MLH1, MSH2 y MSH6. Mutation detection analysis requires the complete sequencing of these genes, given the high frequency of family-specific alterations. A point mutation (2269- 2270insT in the last codon of the MLH1 gene has been detected in families from a northern region of Italy (Reggio Emilia.Given that this alteration was registered only in people from this region, it has been considered a founder mutation. In this work, we present an Argentine HNPCC family

  6. Mercado de trabajo y condiciones de vida en Mendoza a comienzos del siglo XX

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    Juan Manuel Cerdá


    Full Text Available El propósito del presente trabajo es analizar los cambios y las continuidades en el proceso de formación del mercado de trabajo en la provincia de Mendoza a comienzos del siglo XX. La incorporación de un número significativo de inmigrantes a finales del siglo XIX junto a un proceso de reorganización productiva asociado al desarrollo de la industria vitivinícola, implicó cambios en las relaciones sociales y en las condiciones de vida de amplios sectores de la población mendocina. Iniciado el siglo XX, la vitivinicultura se convirtió en la principal actividad productiva de la provincia y la más importante en su rubro a nivel nacional. Los viñateros, productores agroindustriales, industriales bodegueros, contratistas de viñas , etc., fueron constituyéndose en parte de una sociedad cada vez más heterogénea y diversa, producto del desarrollo capitalista que experimentó la región desde el último tercio del siglo XIX y que se insertó en el proceso de incorporación de la economía Argentina al mercado mundial. Este período resulta de suma importancia porque se determinó un sistema productivo en torno a la actividad vitivinícola de la provincia que dio forma al mercado de trabajo regional. En este contexto, la inserción de los trabajadores se dio de una manera muy dispar en el proceso productivo, caracterizado por una alta estacionalidad y una escasa especialización de la mano de obra requerida.The aim of this work is to analyze the changes and continuities during the process of formation of the labor market in the province of Mendoza in the early 1900s. Wide sectors of the Mendoza population saw their life conditions and social interactions change as a result of the absorption of a significant amount of immigrants by the end of 19 th century, together with a restructuring of production connected to the development of the wine industry. Shortly after the turn of the century, wine had become the main productive activity of that

  7. Evolución paleoambiental de la transición glacial-postglacial en la Formación Agua Colorada (Grupo Paganzo, Carbonífero, Sierra de Narváez, NO argentino Palaeoenvironmental evolution of the glacial-postglacial transition in the Agua Colorada Formation (Paganzo Group, Carboniferous, Sierra de Narváez, NW Argentina

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    Carlos O Limarino


    ón postglacial, entre el Sistema del Famatina, la Precordillera y las Sierras Pampeanas.The Carboniferous sequences (lower section of the Paganzo Group outcroping in the central part of the Sierra de Narváez (Las Angosturas area, northwestern Argentina are described in this paper. From the regional point of view, two major Carboniferous sequences have been identified. Firstly, diamictites, conglomerates, sandstones, carbonaceous mudstones and thin coal beds that were included in the Agua Colorada Formation. A second group comprises monotonous sequences of shales and interstratified mudstones and sandstones which were excluded from the Agua Colorada Formation and identified with the informal ñame of 'Marine Late Paleozoic rocks'. Sedimentological characteristics of the Agua Colorada Formation allow recognizing seven facies associations in the Angosturas area: 1. monomictic diamictites; 2. polymictic diamictites and conglomerates; 3. shale-sandstone cycles; 4. dark shales; 5. greenish monomictic conglomerates; 6. channelised polymictic conglomerates and 7. coarse-grained sandstones, shales and thin coal beds. Facies associations 1 and 2, including both massive and rese-dimented diamictites, are interpreted as related to the well known Namurian gondwanic glacial event in western basins of Argentina. Facies associations 3,4 and 5 record the evolution of a fjord environment formed as a consequence of the postglacial transgression (the so-called Namurian postglacial transgression that flooded glacial valleys in the major part of the Paganzo Basin. A regional relative sea level fall marked by a regional incisión surface occurred at the base of facies association 6, and the fjord environment was sharply replaced by fluvial sedimentation (facies associations 6 and 7. A regional correlation model, based on the postglacial transgression key level, among the Sistema del Famatina, Precordillera and Sierras Pampeanas is proposed.

  8. Paleoambientes sedimentarios de la Formación Toro Negro (Neógeno, antepaís fracturado andino, noroeste argentino Sedimentary paleoenvironments of the Toro Negro Formation (Neogene, Andean broken foreland, northwest Argentina

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    Patricia L Ciccioli


    paleovalle fluvial en el norte del área y posterior relleno por cursos fluviales gravo-arenosos provenientes del oeste principalmente (AFI-V. En la etapa II (Mioceno Medio a Tardío se desarrollan sistemas fluviales no confinados areno-gravosos (AFVI-VII que progradan sobre un lago somero (AFVIII desarrollado en el sur del área. Finalmente, la etapa III (miembro superior, Mioceno Tardío-Plioceno Temprano corresponde a pulsos de progradación de la cuña clástica (AFIX-XI desde el oeste (Precordillera.The Toro Negro Formation (Neogene records the sedimentation in the broken-foreland Vinchina Basin during the Andean Orogeny, in northwestern Argentina. This unit is composed of conglomerates, sandstones and mudstones together with some beds of breccias and tuffs deposited mainly in fluvial environments. Eleven facies associations (FA were identified in this unit, eight of them corresponding to the lower member and three to the upper member. FAI is composed of massive intraformational megabreccias and cross-bedded conglomerates deposited in braided fluvial systems that filled a deep fluvial paleovalley formed in the north of the studied region. FAII was only identified in marginal positions of the paleovalley and is composed of intraformational breccias and sandstones forming channel belts incised within alluvial plains deposits. FAIII comprises gravelly channel belts and sandy floodplains dominated by crevasse splays interpreted as deposited in semiarid anastomosing fluvial systems. FAIV shows coarsening-upward successions with thick muddy alluvial plain deposits including thin crevasse splays and gravelly single channels. Encapsulated channel complexes composed of coarse-grained sandstones and scarce conglomerates, form FAV. FAVI covers a low-relief erosive surface and is mainly composed of conglomerates and gravelly sandstones deposited in broad alluvial plains. This fluvial complex evolved to a lower-energy system (FAVII characterized by an increase of muddy floodplain

  9. Automated recognition of quasi-planar ignimbrite sheets and paleo-surfaces via robust segmentation of DTM - examples from the Western Cordillera of the Central Andes (United States)

    Székely, B.; Karátson, D.; Koma, Zs.; Dorninger, P.; Wörner, G.; Brandmeier, M.; Nothegger, C.


    The Western slope of the Central Andes between 22° and 17°S is characterized by large, quasi-planar landforms with tilted ignimbrite surfaces and overlying younger sedimentary deposits (e.g. Nazca, Oxaya, Huaylillas ignimbrites). These surfaces were only modified by tectonic uplift and tilting of the Western Cordillera preserving minor now fossilized drainage systems. Several deep, canyons started to form from about 5 Ma ago. Due to tectonic oversteepening in a arid region of very low erosion rates, gravitational collapses and landslides additionally modified the Andean slope and valley flanks. Large areas of fossil surfaces, however, remain. The age of these surfaces has been dated between 11 Ma and 25 Ma at elevations of 3500 m in the Precordillera and at c. 1000 m near the coast. Due to their excellent preservation, our aim is to identify, delineate, and reconstruct these original ignimbrite and sediment surfaces via a sophisticated evaluation of SRTM DEMs. The technique we use here is a robust morphological segmentation method that is insensitive to a certain amount of outliers, even if they are spatially correlated. This paves the way to identify common local planar features and combine these into larger areas of a particular surface segment. Erosional dissection and faulting, tilting and folding define subdomains, and thus the original quasi-planar surfaces are modified. Additional processes may create younger surfaces, such as sedimentary floodplains and salt pans. The procedure is tuned to provide a distinction of these features. The technique is based on the evaluation of local normal vectors (perpendicular to the actual surface) that are obtained by determination of locally fitting planes. Then, this initial set of normal vectors are gradually classified into groups with similar properties providing candidate point clouds that are quasi co-planar. The quasi co-planar sets of points are analysed further against other criteria, such as number of minimum

  10. Emplacement of the La Peña alkaline igneous complex, Mendoza, Argentina (33° S): Implications for the early Miocene tectonic regime in the retroarc of the Andes (United States)

    Pagano, D. S.; Galliski, M. A.; Márquez-Zavalía, M. F.


    The La Peña alkaline complex (LPC) of Miocene age (18-19 Ma) lies on the eastern front of the Precordillera (32°41ʹ34ʺS, 68°59ʹ48″W, 1400-2900 m a.s.l.), 30 km northwest of Mendoza city, Argentina. It is a subcircular massif of 19 km2 and 5 km in diameter, intruded in the metasedimentary sequence of the Villavicencio Formation of Silurian-Devonian age. It is the result of integration of multiple pulses derived from one or more deep magma chambers, which form a suite of silicate rocks grouped into: a clinopyroxenite body, a central syenite facies with a large breccia zone at the contact with the clinopyroxenite, bodies of malignite, trachyte and syenite porphyry necks, and a system of radial and annular dikes of different compositions. Its subcircular geometry and dike system distribution are frequent features of intraplate plutons or plutons emplaced in post-orogenic settings. These morphostructural features characterize numerous alkaline complexes worldwide and denote the importance of magmatic pressures that cause doming with radial and annular fracturing, in a brittle country rock. However, in the LPC, the attitude of the internal fabric of plutonic and subvolcanic units and the preferential layout of dikes match the NW-SE extensional fractures widely distributed in the host rock. This feature indicates a strong tectonic control linked to the structure that facilitate space for emplacement, corresponding to the brittle shear zone parallel to the N-S stratigraphy of the country rock. Shearing produced a system of discontinuities, with a K fractal fracture pattern, given by the combination of Riedel (R), anti-Riedel (R‧), (P) and extensional (T) fracture systems, responsible for the control of melt migration by the opening of various fracture branches, but particularly through the NW-SE (T) fractures. Five different pulses would have ascent, (1) an initial one from which cumulate clinopyroxenite was formed, (2) a phase of mafic composition represented by

  11. Geodynamic controls on the contamination of Cenozoic arc magmas in the southern Central Andes: Insights from the O and Hf isotopic composition of zircon (United States)

    Jones, Rosemary E.; Kirstein, Linda A.; Kasemann, Simone A.; Dhuime, Bruno; Elliott, Tim; Litvak, Vanesa D.; Alonso, Ricardo; Hinton, Richard


    ))), obtained for the Late Oligocene (∼23 Ma) to Late Miocene (∼9 Ma) magmatic rocks located in the Argentinean Precordillera, and the Late Miocene (∼6 Ma) volcanic rocks present in the Frontal Cordillera. The observed isotopic variability demonstrates that the assimilation of pre-existing continental crust, which varies in both age and composition over the Andean Cordillera, plays a dominant role in modifying the isotopic composition of Late Eocene to Late Miocene mantle-derived magmas, implying significant crustal recycling. The interaction of arc magmas with distinct basement terranes is controlled by the migration of the magmatic arc due to the changing geodynamic setting, as well as by the tectonic shortening and thickening of the Central Andean crust over the latter part of the Cenozoic.

  12. The role of changing geodynamics in the progressive contamination of Late Cretaceous to Late Miocene arc magmas in the southern Central Andes (United States)

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


    -T) basement, both on the basis of their trace and rare earth element compositions and the presence of P-T inherited zircon cores. Crustal reworking is also identified in the Argentinean Precordillera; Late Miocene (12-9 Ma) arc magmatic rocks display distinct trace element signatures (specifically low Th, U and REE concentrations) and contain inherited zircon cores with Proterozoic and P-T ages, suggesting the assimilation of both the P-T basement and a Grenville-aged basement. We conclude that changing geodynamics play an important role in determining the geochemical evolution of magmatic rocks at convergent margins and should be given due consideration when evaluating the petrogenesis of arc magmas.

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

    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

  14. Spatiotemporal variation patterns of plants and animals in San Carlos de Apoquindo, central Chile Patrones de variación espaciotemporal de plantas y animales en San Carlos de Apoquindo, Chile central

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    de Santiago en la precordillera andina. Este sitio atrajo a numerosos investigadores durante 1976-1990 debido a su proximidad a Santiago y a su condición de relativamente protegido. Reviso la literatura y proveo información no publicada sobre este sitio. Un total de 132 referencias bibliográficas describen la ecología de San Carlos de Apoquindo, en alrededor de 30 tópicos. La vegetación arbustiva y herbácea han sido bien estudiadas, pero poco se sabe acerca de sus respectivos bancos de semillas. Entre los animales, los micromamíferos, conejos, y predadores rapaces y carnívoros son los mejor investigados, en tanto que los artrópodos epígeos, anfibios, lagartijas, culebras, aves paserinas y los carroñeros de todo tipo son los menos estudiados. Temáticamente, se han analizado interacciones planta/clima, planta/suelo, planta/herbívoro y herbívoro/predador, así como la descomposición de cadáveres animales. Sin embargo, hay desbalances grandes en la profundidad con que se han tratado estos tópicos. Los aspectos mejor estudiados se refieren a interacciones planta/herbívoro y herbívoro/predador. Hasta ahora, no existía descripción detallada de suelos y clima en el área, que aquí presento. Aprovechando el aspecto de largo plazo de la investigación en el sitio, destaco los patrones de variación temporal. Y aprovechando la presencia de diferentes unidades de paisaje en el sitio, también destaco su variabilidad espacial. En general, San Carlos de Apoquindo ha contribuído grandemente al entendimiento de los procesos ecológicos en Chile central. Llamo a realizar esfuerzos renovados para estudiar la ecología de este sitio desde una perspectiva ecosistémica

  15. Large slope instabilities in Northern Chile and Southern Peru (United States)

    Crosta, Giovanni B.; Hermanns, Reginald L.; Valbuzzi, Elena; Frattini, Paolo; Valagussa, Andrea


    Deep canyon incision into Tertiary paleosurfaces and large slope instabilities along the canyon flanks characterize the landscape of western slope of the Andes of northern Chile and South Peru. This area belongs to the Coastal Escarpment and Precordillera and is formed by coarse-grained clastic and volcanoclastic formations. The area is characterized by intense seismicity and long-term hyperaridity (Atacama Desert). Landslides along the canyon flanks affect volumes generally up to 1 km3 and locally evolved in large rock avalanches. We prepared a landslide inventory covering an area of about 30,000 km2, extending from Iquique (Chile) to the South and Tacna (Peru) to the North. A total of 606 landslides have been mapped in the area by use of satellite images and direct field surveys, prevalently including large phenomena. The landslides range from 1 10-3 km2 to 464 km2 (Lluta landslide). The total landslide area, inclusive of the landslide scarp and of the deposit, amounts to about 2,130 km2 (about 7% of the area). The mega landslides can be classified as large block slides that can evolve in large rock avalanches (e.g. Minimini landslide). Their initiation seems to be strongly associated to the presence of secondary faults and large fractures transversal to the slope. These landslides show evidence suggesting a re-incision by the main canyon network. This seems particularly true for the Lluta collapse where the main 'landslide' mass is masked or deleted by the successive erosion. Other landslides have been mapped along the Coastal Escarpment and some of the major tectonic escarpments with an E-W trend. We examined area-frequency distributions of landslides by developing logarithmically binned, non-cumulative size frequency distributions that report frequency density as a function of landslide planar area A. The size frequency distribution presents a strong undersampling for smaller landslides, due to the extremely old age of the inventory. For landslides larger than

  16. Litterfall, litter decomposition and nitrogen mineralization in old-growth evergreen and secondary deciduous Nothofagus forests in south-central Chile Aporte, descomposición de hojarasca y mineralización de nitrógeno en bosques siempreverdes de antiguo crecimiento y bosques secundarios deciduos, centro-sur de Chile

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    mineralization rates in the present study.Los ecosistemas forestales del sur de Chile presentan un gran valor ecológico pues constituyen una de las mayores áreas del hemisferio Sur con existencias de bosques templados lluviosos. Están sometidos a procesos de deforestación, invasión de especies exóticas, fragmentación e incremento de depositación de nitrógeno (N atmosférico. Para apoyar su manejo sustentable se requiere de mayor conocimiento en el ciclo de nutrientes de estos ecosistemas. Se estudia la dinámica de nutrientes en cuatro sitios de bosques lluviosos valdivianos de la precordillera de los Andes, centro-sur de Chile: un bosque siempreverde de antiguo crecimiento prístino y otro alterado, un bosque caducifolio secundario con manejo silvícola y otro sin. Durante el período octubre 2002 -septiembre 2006, se estimaron (i masa de la hojarasca (cuatro años y contenido de nutrientes de la hojarasca (un año, (ii descomposición y dinámica de nutrientes de hojarasca (un año y de la corteza de Saxegothaea conspicua, y (iii mineralización neta de nitrógeno (N-min en el suelo in situ (un año. El aporte de hojarasca en los cuatro sitios fluctúa desde 3.5 hasta 5.8 ton ha-1 año-1, y es temporalmente menor en bosque caducifolio manejado, respecto del caducifolio sin manejo. Además, presentan una estacionalidad en los siempreverdes que es diferente, respecto de los deciduos. La hojarasca se descompone más rápidamente (promedio 32 % pérdida de masa después de un año que la corteza (8 %, pero no se presentaron diferencias significativas en la hojarasca. El N neto en la hojarasca de los bosques siempreverdes disminuye durante la descomposición, pero se incrementa en la hojarasca de los deciduos. La N-mineralización neta del suelo fue completa en el bosque siempreverde prístino, intermedia en los bosques deciduos y el más baja en el bosque siempreverde alterado. Dada la ausencia de réplicas en las parcelas, no puede ser demostrado el impacto definido del