Synchronism between development of Cenozoic volcanic arcs and back-arc basins: Reasons and consequences

A geographic information system (GIS “Volcanic belts”) was used for analyzing the spatial and temporal relationship between tectono-magmatic cycles in the Cenozoic that took place at the convergent plate boundaries, mostly in volcanic arc-back-arc systems. The onset of back-arc basins and subaerial arc volcanism and their main evolutionary stages are shown to have occurred about the same time. These processes are still ongoing, which is indicated by today’s active volcanoes, high heat flows, and high deep-focus seismicity. The crust underlying both tectonic structures undergoes transformation, which results in a significant thinning of the “granite” layer within the volcanic belts, whereas crust within the back-arc basins changes its properties to the transitional (suboceanic) and oceanic type crusts. All processes that occur at the convergent plate boundaries can be described within the arc-back-arc system, the principal dynamic components of which are the asthenospheric plume upwelling above the continent edge and the oceanward-spreading plume head. This was accompanied by a gradual crustal thinning in the back-arc region and the formation of areas with oceanic crust, as well as by involvement of crustal material, together with rocks of the subducting slab, into subduction processes. As a result, the continental crust is removed from the tectonosphere and stored in the “slab cemetery.” Only a minor portion of the crustal materials is returned to the surface as subduction-related magmatism.