The Structure of the Southern Central Andes (Chos Malal fold and thrust belt).

TURIENZO, MARTÍN; SÁNCHEZ, NATALIA; LEBINSON, F; DIMIERI, L

The making of the Chilean- Argentinean Andes

Springer

Año: 2018; p. 411 - 441

Abstract Based on a compilation of published 2-D velocity-depth models alongthe Chilean margin (22°?48° S), I review the structure and tectonic processes thatgovern this convergent margin in terms of subduction erosion and sedimentaccretion/subduction. North of the collision point between the Juan FernándezRidge with the overriding continental South American plate (Chile at *32.5° S),subduction erosion has been active since Jurassic resulting in large-scale crustalthinning and long-term subsidence of the outermost forearc. Published 2-Dvelocity?depth models show a prominent lateral velocity contrast that propagatesdeep into the continental crust defining a major lateral seismic discontinuity (interpretedas the volcanic-continental basement contact of the submerged CoastalCordillera characterized by a gravitational collapse of the outermost fore arc).Between the Juan Fernández Ridge and the Chile Triple Junction (CTJ) of theNazca-Antarctic-South American plates (Chile at *46.5° S), an accretionary prism5?50 km wide has been formed due to an increase of trench sedimentation triggeredby denudation processes of the Andes after the last Pleistocene Glaciation.However, the relatively small size of the accretionary prism is not compatible withan efficient history of sediment accretion since the Pleistocene, and sedimentsubduction is a dominant process especially south of the oceanic Mocha FractureZone (Chile at *38° S) and north of the CTJ. In the overriding plate, seismicstudies reveal two prominent velocity transition zones characterized by steep lateralvelocity gradients, resulting in a seismic segmentation of the marine fore arc. Thesouthern central Chilean margin is composed of three main domains: (1) a frontalprism at the toe of the continental slope, (2) a paleoaccretionary complex, and(3) the seaward edge of the Paleozoic continental framework that forms part of theCoastal Cordillera. Near the CTJ, where the Nazca-Antarctic spreading center(Chile Rise) collides with the margin, subduction erosion is active, and rapid upliftfollowed by subsidence of the forearc area, normal faulting and intensive sedimentarymass wasting are documented. South of the CTJ, the convergence betweenthe oceanic Antarctic and continental South American plate is slow allowing more time sediment accumulation at the trench enhancing the formation of relativelylarge accretionary prisms (width of 70?90 km).