Abstract

ZAPATA-VILLADA, Juan Pablo; RESTREPO, Jorge Julián; CARDONA-MOLINA, Agustín  and  MARTENS, Uwe. GEOCHEMISTRY AND GEOCHRONOLOGY OF THE BASIC VOLCANIC AND GABROIC ROCKS IN THE ALTAMIRA REGION, WESTERN CORDILLERA OF COLOMBIA: A RECORD OF OVERIMPOSED CRETACEOUS PLATEAU AND OCEANIC ARC ENVIROMENTS. bol.geol. [online]. 2017, vol.39, n.2, pp.13-30. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v39n2-2017001.

Regional paleogeographic models based on limited geochronological and geochemical data from the Western Cordillera of the Colombian Andes have suggest that the exposed Cretaceous magmatic rocks were formed in plateau and intra-oceanic arc environments before their Late Cretaceous-Paleocene accretion to the continental margin. New geochemical and geochronological constraints from volcanic, pyroclastic and intrusive plutonic rocks of the Altamira section in the northern segment of the Western Cordillera record the existence of a former basaltic sequence characterized by an E-MORB signature erupted in a subaqueous to subaerial environment. Such sequence can be correlated to other Early Cretaceous volcanic rocks in the Western Cordillera of Colombia, that together with other exposures in the Ecuadorian Andes and the Caribbean are part of a major oceanic plateau that was formed in the southwestern Pacific region that formed the allochthonous Caribbean plate. This sequence was intruded by gabbroic plutons with a tholeiitic arc affinity signature, that together with other plutons of the Western Cordillera record the formation of an oceanic arc by ca. 88 Ma, as suggested by the new U-Pb LA-ICP-MS zircon ages. Older inherited zircon ages of 95 Ma and 114 Ma found within this gabbroic body correlate with sedimentary and plutonic ages of the host basaltic rocks, confirming the Early Cretaceous timing for the plateau episode. Although more geochronological data is still need from the Western Cordillera, the available temporal and compositional constraints, including the data presented in this contribution, suggest that the timing of the plateau formation episode maybe older than previously suggest, and that an oceanic arc was formed over this plateau before its accretion to the continental margin.

Keywords : U-Pb; Western Cordillera; Oceanic Plateau; gabbroic Plutons; Altamira.

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