G. Yanez

L'analyse flexurale de 15 sections topo-gravimétriques a permis de caractériser la lithosphère andine d'un point de vue compositionnel, structural et thermomécanique. La relation entre les variations longitudinales de ces caractéristiques et la segmentation tectonique de l'orogène permet de spéculer sur les facteurs qui contrôlent la construction et l'évolution des Andes. (Résumé d'auteur

Long-lived, high-angle fault systems constitute high-permeability zones that can localize the upward flow of hydrothermal fluids and magma throughout the upper crust. Intersections of these types of structures can develop complex interference patterns, which constitute volumes of damaged rock (networks of small-scale faults and fractures) where permeability may be significantly enhanced. This is relevant for understanding regional-scale structural controls on the emplacement of hydrothermal mineral deposits and volcanic centers, and also on the distribution of areas of active upper-crustal seismicity. In the high Andes of central Chile, regional-scale geophysical (magnetic, gravimetric, seismic) and structural datasets demonstrate that the architecture of this Andean segment is defined by NW- and NE-striking fault systems, oblique to the N-S trend of the magmatic arc. Fault systems with the same orientations are well developed in the basement of the Andes. The intersections of conju...

ABSTRACT L'analyse flexurale de 15 sections topo-gravimétriques a permis de caractériser la lithosphère andine d'un point de vue compositionnel, structural et thermomécanique. La relation entre les variations longitudinales de ces caractéristiques et la segmentation tectonique de l'orogène permet de spéculer sur les facteurs qui contrôlent la construction et l'évolution des Andes. (Résumé d'auteur)

Extensional basin development (Middle?-Late Eocene to Early Miocene), basin inversion and deformation of the basin fill (Early to Late Miocene) and rapid, high magnitude surface uplift (Late Miocene to Recent) characterize the Cenozoic tectonic evolution of the central Chilean Principal Cordillera, between 33° and 36°S. Extension (Abanico Basin) was associated with crustal thinning and toleiitic magmatism, while basin inversion was

One of the most prominent tectonic features of the Andes is the Central Andean Rotation Pattern (CARP), which is closely related to the Bolivian Orocline and characterized by paleomagnetically determined clockwise rotations in northern Chile and counterclockwise rotations in southern Peru (Arriagada et al., 2008). Along the Chilean margin, between 29°S and 38°S, three prominent curvatures are observed. The Vallenar Discontinuity near ˜29°S corresponds to the southern limit of the Bolivian Orocline. North of 29°S the major structural elements (Paleozoic basement highs and thrusts) are NNE oriented while from 29°S down to 32°S the structures are mainly NS. The central Chilean margin presents also significant bends near Santiago (˜33°S, Maipo Orocline) and in the Arauco region (˜38°S). Near Santiago, the Maipo bend coincides with the subduction of the Juan Fernandez Ridge (JFR). During the last five years we have undertaken new paleomagnetic and structural studies along the forearc of ...

ABSTRACT Au sud des 33° 45', l'arc volcanique du Miocène moyen à supérieur (formation Farellones) est décollé à 2,5 km de profondeur sur sa base méso-cénozoïque. Sa limite occidentale correspond à une zone triangulaire, entre chevauchement et rétrochevauchement. (Résumé d'auteur)

Based on data from a dense local temporary seismological network, crustal seismicity is characterized, and a 3- D body wave velocity structure is obtained by tomographic inversion down to the subducted slab. In the framework of Fondecyt 1050758, GeoAzur-IRD and ACT-18 projects, 35 broadband and short period instruments, were deployed in the studied zone for 135 days recording in continuous mode. At this zone the Andean active volcanism reappears after a gap of volcanic activity since late Miocene occurring north of 33 S due to the Central Chile flat slab subduction zone. Crustal seismicity in the depth range 0-30 km is well correlated with known geological faults that become now important in the assessment of the regional seismic hazard. This seismicity also clusters around the giant porphyry cooper deposits in the region (Rio Blanco, El Teniente), and are neither related to mine-blasts nor induced by mining activity. Moreover, the local 3-D velocity structure shows that the zone surrounding each deposit is characterized by high Vp/Vs greater than 1.8, which may indicate fluid phases located in the weakest and more fractured zone of the crust. The body wave velocity pattern shown at depth by the local tomography indicates channels of high Vp/Vs connecting the subducted slab with the surface at places where active volcanism is present, suggesting upward migration of hydrous or melted rocks. This pattern agrees with the one observed with a previous regional tomography that includes this zone, while this Vp/Vs pattern tends to be horizontal at the flat slab zone. At depths of 20-25 km, a layer of high Vp/Vs is observed beneath the Andes Cordillera that could be associated to changes in the rheological properties between the upper and lower crust, or to accumulation of magma. The average stress tensor, derived from focal mechanisms, indicate that the Andean zone is under compression in the plate convergence direction.

Au sud des 33° 45', l'arc volcanique du Miocène moyen à supérieur (formation Farellones) est décollé à 2,5 km de profondeur sur sa base méso-cénozoïque. Sa limite occidentale correspond à une zone triangulaire, entre chevauchement et rétrochevauchement. (Résumé d'auteur)

Con la ayuda de un analisis flexural de la correlacion entre relieve y gravedad, se investiga que factores controlan la segmentacion del sistema de convergencia andino entre los 15 y 47°S y como ellos interactuan en terminos del proceso orogenico. Como base de este analisis, se propone inicialmente una definicion de segmentacion; en un primer orden se distingue entre Andes centrales (15-33,5°S) y Andes del sur (33,5 -47°S). A lo largo de ambas unidades mayores se diferencian segmentos de segundo orden; Altiplano (15-23°S), Puna (23-28°S) y Cordillera Frontal (28-33,5°S) en los Andes centrales, Cordillera Principal (33,5-39°S) y Cordillera Patagonica (39-47°S) en los Andes del sur. Los resultados del analisis flexural sobre este esquema de segmentacion tectonica indican variaciones espaciales del espesor elastico Te (el cual determina la rigidez de la litosfera), del espesor cortical EC, y de la fuerza compresiva horizontal F. Te es alto en el antearco y antepais y bajo en el eje del orogeno, presentando valores minimos (<10 km) y un fuerte gradiente transversal en los Andes Centrales. En contraste, el valor minimo de Te en el segmento Cordillera Patagonica es del orden de 35 km. Temuestra una correlacion inversa con EC, parametro que alcanza su maximo en el sector occidental de los Andes centrales (65-70 km). A su vez, F presenta valores maximos en los extremos norte y sur de los Andes centrales (hasta 4 x 1012 N/m), consistente con el alto acoplamiento interplacas existente en estos sectores. Desde un punto de vista reologico, Te es directamente proporcional tanto a la razon entre plagioclasa y cuarzo en la corteza como a la razon entre tasa de deformacion y flujo calorico impuesta por la convergencia. Esta relacion cualitativa, complementada por los controles geologicos y geofisicos existentes, permite sugerir que la segmentacion andina de primer orden es causada por el contraste composicional entre la corteza felsica de los Andes centrales y otra mafica de los Andes del sur. La segmentacion de segundo orden se asocia ademas con variaciones del regimen termomecanico ligado al proceso de convergencia.

... Fig. 4. The Cerro Llaretas Triangle Zone. Note ... Co. through this range) of an incipienttriangle zone in which gently folded 'Abanico' beds fill the wedge. Deformation increases southward but no passive roof duplex is yet developed. ...

... Angamos 0610, Antofagasta, Chile jcembrano@ucn.c. Armando Siña. ... According to Matthews et al. (1995) fractional crystallization of a highly oxidized magma, without an early releasing of gases, would lead to the formation of a sulphur-rich mineralized hydrothermal fluid. ...

... Será tarea de otros, con una aproximación o metodología más apropiada (eg, Ballard et al., 2002), el confirmar o rechazar las ideas rudimentariamente expresadas en este artículo, cuya validez creemos no se ve afectada por las precisiones metodológicas del colega ...

... Angamos 0610, Antofagasta, Chile jcembrano@ucn.c. Armando Siña. ... According to Matthews et al. (1995) fractional crystallization of a highly oxidized magma, without an early releasing of gases, would lead to the formation of a sulphur-rich mineralized hydrothermal fluid. ...

... Fig. 4. The Cerro Llaretas Triangle Zone. Note ... Co. through this range) of an incipienttriangle zone in which gently folded 'Abanico' beds fill the wedge. Deformation increases southward but no passive roof duplex is yet developed. ...

Two temporary networks were deployed for about 100 days in the flat-slab subduction zone of Central Chile from Nov. 1999 to Feb. 2000 (30-32S, 70-71.5W; 38 SP stations), and in the transition zone from flat-slab to steep subduction zone of Central Chile-Western Argentina from Nov. 2002 to March 2003 (31.5-34S, 67-71.5W; 29 BB stations). Both networks recorded in continuous mode

From Nov. 2002 to March 2003, the CHARSME project (CHile ARgentina Seismological Measurement Experiment) took place in Chile and Argentina in order to analyze the regional seismotectonic characteristics and to map the change of the subducted Nazca plate from a flat-slab to an inclined geometry. Local seismological and gravimetric data were collected. A seismic network of 30 portable broadband stations,