Ecuador is part of the northern Andes. From east to west, it comprises the Oriente basin , the Andean Cordilleras and the Coastal zone (Fig. J). The Andes of Ecuador consist of two cordilleras separated by the interAndean valley. The Western Cordillera and Coastal zone are mainJy composed of accreted oceanic terranes of Cretaceous to Eocene age , which consist of crustal fragments of oceanic plateaus, locally overlain by isJand arcs, that accreted to the passive margin of Ecuador between 80 and 40 Ma (Fig. 2, Jaillard et al. 2000, Mamberti et al. 2004). From the latest Eocene onwards, a continent-based arc developed first in the Western Cordillera and then, farther east. Since the Oligocene, dextral transpressive kilometer-scale faults crosscut the Western Cordillera and exhumed slices of magmatic and metamorphic rocks, thus sampling the deep levels of the Western Cordillera. The exhumed metamorphic rocks are amphibolites, granulites, and garnet-bearing metasediments. Lherzolites, pyroxenites, harzburgites, as weil as gabbros, basalts and radiolarian cherts have been also recognized. The aim of this study is (i) to characterize the protoliths of the exhumed metamorphic and ultramafic rocks, (ii) to determine their thermodynamic evolution and (iii) to characterize the magmatic affinities of the gabbros and basalts.