Structural control on magmatism along divergent and convergent plate boundaries: Overview, model, problems

Plate boundaries are the most active, unstable and hazardous areas on Earth. The aim of this study is twofold. 1) Provide an overview of the main structural features along divergent and convergent plate boundaries and their relationships to volcanism. The considered divergent plate boundaries include the continental East African Rift System (EARS), the transitional Afar Rifts and slow (Iceland) and fast (East Pacific Rise) oceanic ridges. The analysis of the convergent plate boundaries refers to the extensional (Taupo Volcanic Zone, New Zealand), strike-slip (Sumatra), contractional (NE Japan) and more complex (Central Andes) volcanic arcs. 2) Propose an original and innovative frame to understand tectono-magmatic processes along plate boundaries, based on two major points. a) Magmatism may effectively control the development of plate boundaries. At immature continental divergent plate boundaries (as the non-magmatic portions of the EARS), regional extension plays a major role in extending the upper crust; however, along mature continental and oceanic rifts magmatism is most effective in spreading plates apart through dikes. At convergent plate boundaries, the possibility to develop extensional, strike-slip, contractional and oblique systems along the volcanic arc provides highly variable structural conditions controlling magmatism. At least three magmatic processes (diking, sill emplacement, heat-induced strain localization) may control the development of volcanic arcs. In addition, megathrust earthquakes may induce transient extension, enhancing volcanism. Therefore, the evolution of both divergent and convergent plate boundaries is significantly magma-controlled and magmatic processes seem largely self-sustained, requiring limited direct tectonic contribution; and b) magmatism along divergent and convergent plate boundaries usually focuses in magmatic systems, associated with a dominant volcano. Magmatic systems provide a convenient framework to relate the geometric and compositional features of a magmatic plate boundary to its tectonic setting. In particular, the larger the opening rate, the lower is the aspect ratio A (A = width W/length L) of the magmatic system. Therefore, the linear magmatic accretion of divergent plate boundaries and extensional arcs is replaced by a punctifonn accretion in contractional arcs. Several aspects (magmatic rates, lateral vs. vertical dike propagation along divergent plate boundaries, structural control on volcanism along strike-slip arcs) are still poorly defined and should be the target of future research. (C) 2014 Elsevier B.V. All rights reserved.