Petrological and geochemical characteristics of metamorphic and igneous units from the allochthonous Madre de Dios Terrane, Southern Chile

Abstract

The Denaro Complex, part of the Madre de Dios Terrane is composed of metamorphosed pillow basalts, metahyaloclastites, banded metalliferous and radiolarian metacherts, metapelites and redeposited calcareous metasandstones. The basaltic rocks show primary textures, minerals and structures. They are foliated especially in the vicinities of thrust faults, interpreted to have developed during the accretion of the terrane to the Gondwana margin. Composition of relic primary augite and chromite crystals plots into the MORB field of tectonic discriminant diagrams, as do the analyses of whole rock geochemistry, which indicates that these rocks are akin to volcanic rocks erupted along a constructive plate margin (N- and E-type MORBs), probably in a spreading axis-centered oceanic plateau or ridge. The metamorphic assemblages of pumpellyite–actinolite facies bear witness of metamorphism in a frontal accretionary wedge at elevated P and low T conditions, probably related to the Late Triassic–Early Jurassic Chonide event, which has been recognized elsewhere in the Patagonian Andes.