Crustal melting by ponding of mafic magmas: A numerical model

Abstract

We examine the possibility that an abating period of mantle-related volcanic activity at continental margins triggers the production of crustal-derived melts. A vertical zone, permeated by rising mafic melts, is established below the volcanic arc if long-lasting mantle-derived magmatism occurs. This situation can be assumed to exist at continental arcs. We propose that mafic magmas release heat and water into the crustal environment, if subsequent magma ascent is stopped due to establishment of a density barrier. This process enhances intracrustal partial melting. Using a finite-element program, we simulate in a 2D model area the time-dependent change of the crustal thermal structure. The spatial distribution of potential melting zones and their degree of partial melting within the crust is computed. The amount of generated melt able to segregate is calculated and compared with volume estimates given by field investigation and geochemical constraints in a natural test case. We chose the Altiplano–Puna volcanic complex (APVC) which is part of the central Andes, as an example where the process may have happened and show, from simple approximations, that the model can explain the volumes of crustal melts represented by the felsic volcanics in this region. Although the model parameters and assumptions used are specific to this geologic context, the proposed model is generally applicable to any arc setting.