Magmatic Evolution of the Andes: the contributions of the IGCP Project 120

Abstract

The launch in the early 1970?s of the project 120 ¨Magmatic evolution of the Andes¨ withinthe framework of the International Geological Correlation Program, a joint effort of the InternationalUnion of Geological Sciences and Unesco was timely created and driven from its origins by Umberto Cordani. The Andean-tectonic model had been recently proposed and many unknowns arose to explain the development in time and space of magmatic arcs. Project 120 in ten years of work, contributed with more than 2000 ages and studied throughout the Andes the variations of these arcs. The data provided established that the migration to the foreland of the volcanic arcs was due to crustal erosion by subduction of the forearc and to changes in the geometry of the subducted slab. Each of these processes has different geochemical and petrological characteristics and different time dynamics. In turn, trench arc migrations, especially when they were abrupt and associated with metamorphism and deformation, were indicating the collision of allochthonous terranes on the continental margin. Geochronological and petrological studies carried out in a series of transects allowed identifying the collision of island arcs in the Meso-Cenozoic of the Northern Andes and the accretion of continental terranes in the Paleozoic throughout all the margin. The variation of the geometry of the subducted slab could reach a flat-slab stage with an important gap in magmatism. The study of these and other processes was carried out through intense cooperation between scientists from different Andean countries. Although the scientific results of the project were important, the main legacy of IGCP 120, is tohave established cooperation networks among the participants, which are still successfully maintained in different new programs.