CENOZOIC TECTONIC EVOLUTION OF THE ACTIVE CONTINENTAL-MARGIN OF NORTHERN ANTOFAGASTA, CHILE

The active continental margin of Antofagasta, in Northern Chile, can b e divided into three morphostructural domains. These are from east to west: Coastal Cordillera, coastal platform and Continental slope. The boundary between the Coastal Cordillera and coastal platform is the co astal scarp ca. 1.000 m high. The origin of this remarkable morphologi c feature is the result of a strong marine erosion that was enhanced b y the extreme aridity of Northern Chile. In the Coastal Cordillera a s et of north-south trending faults controls a geometry of asymmetric te ctonic blocks and basins. The youngest faults exhibit kinematic indica tors for sinistral transcurrence. The coastal platform, Mejillones Pen insula and continental slope show the effects of an extensional tecton ics since the Miocene. In all three main domains, the extensional tect onics has controlled the sedimentation in which the finger print of th e tectonic history of the continental margin. The extensional tectonic s is here interpreteted as the result of a tectonic erosion that acted under the Southamerican plate during most of the Mesozoic and Cenozoi c. This tectonic erosion is responsible for the collapse of the Contin ental margin towards the Chile-Peruvian trench. It is believed that th e start of this massive collapse is contemporaneous with the Miocene m arine transgression. An important part in this collapse is taken by th e Antofagasta Fault, that is the material fracture feature against whi ch the collapse took place. It is concluded that the youngest transcur rent sinistral displacements along longitudinal faults in the Coastal Cordillera are only local phenomena. and cannot be related to the mass ive collapse of the Continental margin, nor to the oblique subduction vector, which at present, has an east northeast direction.