INFLUENCE OF THE SUBDUCTION OF THE CARNEGIE VOLCANIC RIDGE ON ECUADORIAN GEOLOGY: REALITY OR FICTION?

The proposed ages for the Carnegie ridge-trench collision, offshore Ecuador, lie in the range between 1 to 15 Ma. Nevertheless, many geological features of Ecuador are commonly referred to as being caused by the Carnegie ridge subduction. To highlight this correlation the following ideas have been expressed by various authors at various times: 1) A flat slab induced by ridge buoyancy 2) Andean cooling rates suggesting that the Carnegie ridge collided with the trench at ~15 Ma and that subsequent interplate coupling produced high exhumation rates at ~9 Ma. 3) The oblique convergence and the subduction of the Carnegie ridge have been proposed to be at the origin of the northward drifting of the North Andean block and the opening of the Gulf of Guayaquil. 4) Several uplift periods from Late Miocene to Early Pleistocene along the fore-arc have been proposed as ridge induced 5) Subduction-related erosion occurring at the Ecuadorian continental margin which is being uplifted in the present day. 6) The chemistry of the active volcanic arc has been linked to the Carnegie ridge's arrival to the trench axis, invoking a flat slab model. As such, an adakitic signal has been interpreted as being ridge-induced. An extensive literature review of the geological evolution of the Northern Andes allow us to suggest that there is no clear segmentation of the deformation linked with the Carnegie ridge subduction area or with its postulated landward prolongation at depth. The presence of a flat slab beneath Ecuador is dubious and abundant evidence arises from numerous studies documenting that adakites in the Andes can be explained by alternative model. Beyond the uncertainty of the flat slab at depth, the along strike segmentation of the Andean chain is questionable. Indeed, widespread cooling events have been observed in the Andes for at least the past 25 Ma they possibly represent an ongoing process. There is no one specific cooling period linked with the Carnegie ridge's subduction.