SPREADING-SUBSIDENCE AND OCEANIC PLATEAU ACCRETION DURING THE CRETACEOUS EVOLUTION OF WESTERN COLOMBIA

Plate evolution models considered two belts in the West Colombian Andes: Neoproterozoic Metamorphic Rocks of Continental Affinity (NMRCA) to the east and Cretaceous rocks of oceanic affinity to the west, separated by the Romeral Fault. Further work found three belts to the west of the NMRCA: (1) the Quebradagrande Complex (Cx), a strip of igneous and Albian-Aptian sedimentary rocks of oceanic affinity (2) the Arquía Cx, an amphibolites and green schist belt of medium pressure and oceanic affinity; and (3) the Western Cretaceous Lithospheric Oceanic Province (WCLOP), Upper Cretaceous mafic and ultramafic igneous and sedimentary rocks. Colombia's geological mapping uses the Romeral Fault name for boundaries between these belts creating confusion and new names are proposed: the San Jerónimo Fault between the NMRCA and the Quebradagrande Cx; the Silvia-Pijao Fault between the later and the Arquia Cx, and the Cauca-Almaguer Fault, between the Arquia Cx and the WCLOP.

The Arquia Cx age causes controversy; but this belt, and the NMRCA are intruded by Permo-Triassic plutons. Two interpretations suppose that: (1) it is older than Permo-Triassic as it hosts plutons; and (2), that the Arquia Cx and the NMRCA, were forming a single province in the magmatic event originating the plutons.

Geochemistry of mafic volcanic rocks of the Quebradagrande Cx and of the WCLOP, show these units generated in different geotectonic settings. The Quebradagrande Cx includes volcanic rocks of calc-alkaline affinities enriched in LILE relative to HFSE, typical of rocks generated in supra-subduction zone mantle wedges. The WCLOP includes basalts of tholeitic affinities with both flat incompatible multielement and REE patterns proper of oceanic plateaus. The Quebradagrande Cx represents an intracratonic marginal basin produced by spreading-subsidence of an active continental margin, where thinning of the lithosphere ended up generating oceanic crust. This spreading would have caused continental margin split separating the Arquía Cx from the NMRCA and generating the Quebradagrande Cx in between. This basin would have been trapped during the collision the WCLOP, accreted to the West of the Arquía Cx, in the Early Eocene. Collision produced an accretionary complex where rocks of different crustal level rocks mixed generating a milonite belt