NEOTECTONIQUE DE L'ARC VOLCANIQUE QUATERNAIRE DES ANDES DU SUD DU CHILI ENTRE 37° ET 42° S

Abstract : The Southern Andes in Chile occur along the active margin between Nazca and South American plates and they are a global result of the oblique convergence since the Cenozoic. Quaternary volcanic arc, there represented by the Southern Andean Volcanic Zone (SVZ: 33°-46ºS) shows an architecture that can be related with the crustal deformation along the convergent margin. The southern provinces of the SVZ between 37ºS and the Chile Triple Junction (46ºS), occur next to the Liquiñe-Ofqui Fault Zone (LOFZ), a long-lived intra-arc system. Specifically, the arc segment between 37°-42°S is formed by several oblique volcanic chains and clusters of monogenetic cones located atop of the LOFZ, which are a result of the interaction between magmatic and tectonic processes in the arc.
Neotectonic study of the volcanic arc between 37°-42°S, together with the analysis of the main features of volcanism in the region, allow to establish a rather complex interaction, beside the close spatial relationship between volcanoes and faults. First of all, the influence of the prefractured continental crust that underlies the arc should be remarked. The previous arc geometry and the basement anisotropy exert a strong control on the magma ascent, as can be observed on the Puyehue-Cordón Caulle Volcanic Complex case-study.
Quaternary stress regime, characterised by a dextral transpression with a NE-SW-striking maximum horizontal stress (σ1=σHmax), controls specially the distribution and magmatic evolution of the Holocene oblique chains and the flank cones of stratovolcanoes as well. This regional stress regime locally deviates according to basement structure. In addition, compressive stress tensors can partially explain the relative uplift that can be observed on the first order morphology of the Andean orogen. These vertical displacements can be related to discrete volcanic events that would pump primitive magmas directly from the asthenospheric source.
However, both transpressional and compressive tensors have a constant NE-SW- striking σ1 (σHmax), which support the regional influence of crustal tectonics on magma ascent and volcanism.
With minor frequency, remote seismic triggering by large subduction earthquakes is an additional factor that could explain some volcanic episodes and superposes to the ongoing crustal stress regime along the arc.
Lastly, the regional-scale study of the stress regimes and the volcanic features of arc segments allow understanding how the complex arc architecture is configured and how the mass transfer occurs through the crust.
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Applied geology. Université Paul Sabatier - Toulouse III, 2006. French


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Submitted on : Wednesday, January 10, 2007 - 4:01:00 PM
Last modification on : Thursday, March 12, 2015 - 12:03:00 PM

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Luis Enrique Lara Pulgar. NEOTECTONIQUE DE L'ARC VOLCANIQUE QUATERNAIRE DES ANDES DU SUD DU CHILI ENTRE 37° ET 42° S. Applied geology. Université Paul Sabatier - Toulouse III, 2006. French. <tel-00123663>

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