U-PB AND HF LA-ICP-MS ZIRCON RESULTS FROM PALEOGENE MAGMATIC AND SEDIMENTARY ROCKS OF THE NORTHERN ANDES: TECTONIC IMPLICATIONS FOR WIDE MAGMATIC ARCS DURING SUBDUCTION INITIATION

Basin and provenance analysis on the Northern Andes have suggested the existence of Paleogene magmatic flare-up in the Colombian Andes that seems to have influence the margin for mor than 400 Km. This magmatic record has been related to the early phases of subduction of the Caribbean plate under the South American continent. New Laser Ablation Simultaneous Stream (LASS) U-Pb and Hf isotopic data from plutonic and sedimentary rocks of the western, central and eastern Cordillera of the Colombian Andes show the existence of three crustal domains: western (º_Hf10-14),central (º_Hf1-8) and eastern (º_Hf-15-8). The spatial distribution of these different Hf isotope signatures may be related to the existence of contrasting and different magmatic focuses within the upper continental plate. Altough plate tectonic reconstructions of the Northern Andes suggest that the Caribbean plate was subducting since the Early Paleocene. Evidences of Eocene compressional regime in the Eastern domain contemporaneous with magmatic activity and the still limited subduction advance of the Caribbean plate by the Middle Eocene invokes a distal lithospheric folding probably link to the re-accomodation of mantle dynamics during the early stages of subduction to explain the wide distribution of magmatico focus.