Thermal Structure of Crust and Mantle under Southern Peru as Inferred from Andean Volcanisms

Abstract

Recent volcanic activity along the Peru-Chile Trench distributes regions of thick crust and of a 30-degree dipping slab. Instead, the flattened slab region corresponds to the non-active volcanic region, i.e. the volcanic gap. Differences of crust and mantle structures seem essential to the present distribution of volcanic activity. The dehydration of subducted oceanic crust and the potential melting in the wedge mantle are in general necessary conditions to generate the andesitic magma. However, the most probable source region of “Andean” andesite in the central Andes is the lower crust below about 50 km, because of temperature structures deduced from crust and mantle structure underlain by subducting slab, and from heat flow values of higher than 90 mW/m² in the active volcanic region. The volcanic gap can be explained by the thermal structure due to the subduction of cold flattened slab, that is, temperature distributions could not become high enough to generate andesitic magma in the wedge mantle and the lower crust. It could not be denied the possibility that the partial melting in the lower crust due to the released water would occur without extensive active volcanism.