READING THE FRAGMENTARY RECORD OF LATE CRETACEOUS TO EOCENE ARC-CONTINENT COLLISION AND SUBDUCTION INITIATION IN THE SOUTHERN MARGIN OF THE CARIBBEAN

Arc continent-collision has played a major role in mountain building and modification of the continental crust. In continental margins characterized by continuous convergence, understanding their various effects may be mask by overimposed tectonic events.

In northern South America the Late Cretaceous to Eocene interaction of the Caribbean plate against the South American margin was responsible for the collision of an oceanic arc and a thick plateau-like crust against the continental margin.

Subsequent oblique tectonics has dismembered this orogen leaving different and unique pieces to trace different stages and styled for the transition from collision to subduction installation.

New and recently published evidenced from metamorphic, magmatic and sedimentary units along the margin are used to trace the different stages associated to this major tectonic evolution.

The collision is recorded in Late Maastrichtian to Early Eocene low to middle grade metamorphosed passive margin sediments and associated inversion of the continental basement, local mélange formation and emplacement of peridotites and some minor remnants of intra-oceanic arc rocks.

Subduction initiation and short term installation of a thick Caribbean slab under the South American margin is mark by additional thickening and melting of the formerly accreted oceanic arc, the installation of ca. 10 Ma (60-50) magmatic arc with associated exhumation and subsidence in the upper plate. In some segments of the margin polarity reversal was also responsible for extensional collapse near the suture and the formation of post-collisional basins and the final submergence of the former topography.

Within inland basin of eastern Colombia, major sedimentologic changes (provenance) and basin inversion events seems to be more dramatic in the Late Paleocene-Eocene, contemporaneous with the new subduction record. This pattern reflect contrasting strain pattern, with the earlier arc-continent collision been oblique and therefore causing less effects in the upper plate than the subduction record which suggest more extensive interactions between the converging plates.