CONTRASTING TECTONIC BEHAVIORS OF JURASSIC AND NEOGENE CONTINENTAL ARCS IN THE COLOMBIAN ANDES

The evaluation of the spatio-temporal and compositional characteristics of the Meso-Cenozoic magmatic arcs in the Northern Andean accretionary orogen can be used to understand orogenic phases, and evaluate the major controls that affects the long-term evolution of continental arcs.

An integration of new and published geochronology, geochemistry and isotopic constraints, suggest that that the widespread Jurassic magmatism evolve from an initial phase of strong crustal and lithosphere input in the Early-Middle Jurassic towards a more astenospheric input (high initial Sr ratios and εNd values). The spatial distribution and its association with contemporaneous sedimentary basins also show that the areal extension of both elements was also reduced trough time.

In contrast the Neogene arc in southern Colombia is characterized by inboard arc migration between ca. 21 Ma and the Present, the formation of several major ignimbrite provinces, and a significant reduction in magmatic activity between ca. 9-5.9 Ma. This magmatism was also associated with exhumation and deformation in the adjacent retro-arc basins and fore-arc uplift.

It is suggested that the Jurassic arc was initially controlled by the re-organization of the subduction zone following the Pangea break-up, in which mantle flow and slab roll-back control magma volumes and their composition. Following this stage, plate obliquity became the most important factor and the arc turned to an astenospheric dominated compositional signature until it experienced a major diminish of its magmatic activity in the Late Jurassic.

In contrast, the Neogene arc include involve significant input from subducted sediments, it also controlled by temporal shallowing of the slab, that was apparently influenced by the subduction the relatively young and buoyant Nazca oceanic plate.