Distribution of Temperature and Strength in the Central Andean Lithosphere and Its Relationship to Seismicity and Active Deformation

We present three-dimensional (3D) models of the present-day steady-state conductive thermal field and strength distribution in the lithosphere beneath the Central Andes. Our primary objective was to investigate the influence that the structure of the Central Andean lithosphere has on its thermal and rheological state, and the relationship between the latter and the active deformation in the region. We used our previous data-driven and gravity-constrained 3D density model as starting point for the calculations. We first assigned lithology-derived thermal and rheological properties to the different divisions of the density model and defined temperature boundary conditions. We then calculated the 3D steady-state conductive thermal field and the maximum differential stresses for both brittle and ductile behaviors. We find that the thickness and composition of the crust are the main factors affecting the modeled thermal field, and consequently also the strength distribution. The orogen is characterized by a thick felsic crust with elevated temperatures and a low integrated strength, whereas the foreland and forearc are underlain by a more mafic and thinner crust with lower temperatures and a higher integrated strength. We find that most of the intraplate deformation coincides spatially with the steepest strength gradients and suggest that the high potential energy of the orogen together with the presence of rheological lateral heterogeneities produce high compressional stresses and strong strain localization along the margins of the orogen. We interpret earthquakes within the modeled ductile field to be related to the weakening effect of long-lived faults and/or the presence of seismic asperities.Fil: Ibarra, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Prezzi, Claudia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Bott, Judith. German Research Centre for Geosciences; AlemaniaFil: Scheck Wenderoth, Magdalena. German Research Centre for Geosciences; AlemaniaFil: Strecker, Manfred. Universitat Potsdam; Alemani

Meteoric fluid‐rock interaction in Variscan shear zones

AbstractVariscan shear zones in the Armorican Massif represent sites of strong fluid‐rock interaction. The hydrogen isotope composition of muscovite (δDMs) from syntectonic leucogranite allows to determine the source of fluids that infiltrated the footwall of three detachment zones and the South Armorican Shear Zone. Using temperatures of hydrogen isotope exchange estimated from microstructural data, we calculate the hydrogen isotope ratios of water (δDwater) present within the shear zones during high‐temperature deformation. A ~40‰ difference in δDwater values from deep to shallow crustal level reveals a mixing relationship between deep crustal fluids with higher δD values that range from −34 to −33‰, and meteoric fluids with δD values as low as −74‰ in the upper part of detachment footwalls.</jats:p

Sedimentación intermareal en la bahía de San Sebastián, Tierra de Fuego, Argentina

[ES] La Bahía de San Sebastián se encuentra situada al NE de la Isla Grande de Tierra del Fuego, en la costa atlántica. Tiene forma semicircular con dimensiones de unos 55 km de N a S y de unos 40 de E a W; el rango mareal oscila entre 3,2 y 10,5 m. Existen dos áreas de sedimentación características muy diferentes: la Península del Parámo, formada por playas de gravas y la bahía, propiamente dicha, cuya zona intermareal tiene una anchura de 7 a 10 km durante la marea baja equinoccial, en la que se pueden diferenciar las siguientes áreas de sedimentación: llanuras mareales fangosas; llanura de cheniers con llanura fangosa; playa de arenagrava y llanura mareal mixta; costa acantilada sin sedimentación apreciable y complejo playa-lagoon. El viento del W, que supera los 60 km más de 200 días al año es otro factor dominante en los procesos de sedimentación del área, sobre todo en su parte más alta.[EN] The Bay of San Sebastian is part of the NE atlantic coast of Isla Grande de Tierra del Fuego, Argentina. It is a semicircular embayment 55 km long and 40 km wide. Tidal range varies from 3,2 to 10,5 m. There are two diferent environments: The Península del Páramo, formed by gravel beaches and the Bay S.S., with intertidal flats up to 10 km wide and the following subenvironments: muddy tidal flats, chenier plain, gravel beaches, rocky cliffs and a barrier beach-lagoon complex. The wind blows from the W for more than 200 days per year with speeds in excess of 60 km/h, and controls the sedimentation in the upper part of the flats.Este trabajo es una contribución al proyecto de investigación cooperativo del C.S.I.C. (España) y el C.O.N.I.C.E.T. (Argentina) y al proyecto 1378/82 de la C.A.I.C.Y.T.Peer reviewe

Basin fragmentation controlled by tectonic inversion and basement uplift in Sierras Pampeanas and Santa Bárbara System, Northwest Argentina

The study area is located within the Central Andes, a complex region composed of different structural styles. The region is characterized by highly elevated basement cored ranges, which abruptly break the foreland plain. These ranges were uplifted mainly by deep detached high-angle faults or by the inversion of former extensional faults of the Cretaceous rift. Palaeozoic orogenies generated crustal scale discontinuities in the basement, some of them reactivated during the Andean orogeny. Sedimentary sequences and layers architecture in the basins bordering ranges recorded the tectonic evolution of the region. Basement, syn-rift, postrift and three foreland stages were interpreted in the seismic sections according to the arrangement of the horizons and the main outcropping geological units in bordering ranges. Based on seismic data sets and field data, here we document a particular style of activation of basement faults. Thick-skinned structures that are not always related to the tectonic inversion but to the reactivation of older basement anisotropies represent a paradox since they were not active during the rifting stage. A flat slab subduction and a subsequent angle recovery conditioned the structural evolution of the area