Abstract

The nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics. The Southern Andes volcanic zone (SVZ), located at the obliquely convergent Nazca-South America plate margin between 33°S and 46°S, offers a unique opportunity to address this question because of along-strike changes in crustal thickness, tectonic style and well-constrained long-term and short-term kinematic history. The complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems. Main first-order factors accounting for the along-strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major, intra-arc fault system, the Liquiñe-Ofqui fault zone (LOFZ). Second order factors include the local nature of the volcanic arc basement. Two main categories of volcano-tectonic associations have been identified, according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second-order active/inactive basement faults. Kinematically-coupled associations, those that are directly related to the current dextral transpressional tectonic regime, include NE-trending volcanic alignments of stratovolcanoes and/or monogenetic cones; kinematically uncoupled associations, in which coupling with the current regime is not required, include stratovolcanoes built on top of ancient reverse and strike-slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the LOFZ. Whereas mostly primitive magmas are found in the first category, more evolved terms can occur genetically associated with the second category. We propose a simplified, three-dimensional model for the magma plumbing system along and across the SVZ that integrates kinematically-coupled and kinematically uncoupled volcano-tectonic associations within the framework of first- and second-order geological and structural constraints. © 2009 Elsevier B.V. All rights reserved.