Kimmeridgian to Paleocene Tectonic and Geodynamic Evolution of the Peruvian (and Ecuadorian) Margin

Abstract

Three main tectonic periods are recognized between Kimmeridgian and Paleocene times in the Peruvian-Ecuadorian margin. The “Virù” period comprises a Kimmeridgian event probably equivalent to the Araucan phase of Argentina and Chile, a Tithonian phase related to terrane accretions and collision tectonics along the Ecuadorian margin and to a sudden extension along the north Peruvian margin, and a Berriasian event most probably originated by the incipient South Atlantic rifting. The “Mochica” period begins with tensional and volcanic precursor events (Late Aptian- earliest Albian). It continues with extensional effusions of coastal, back-arc or arc volcanic centres, which alternate with compressive crises (Early and Middle Albian). It ends with the accretion and deformation (thrusting?) of the Albian volcanic arc or back-arc volcanic system (Late Albian-Early Middle Cenomanian). The “Peruvian” phase starts with a paleogeographic change probably triggered by the incipient coastal uplift (Turonian-Coniacian boundary), and continues in the Late Coniacian-Early Santonian with the initiation of northeastward overthrusts located at the southwestern boimdary of the western Trough. It culminates in the latest Campanian, with the creation of intermontane basins which express the onset of the southwestern thrusts, and of foreland basins related to the onset of new overthrusts located at the northeastern boundary of the western Trough. An extensional regime was probably dominant during latest Jurassic and Early Cretaceous times, leading to formation of the main sedimentary basins, with an apparent quiescence of the subduction-related volcanic systems. In Late Aptian times, the rapid convergence and rejuvenation of the subducted lithosphere induced a general compressional and/or wrenching regime, triggering the continentalward migration of the trench and the subsequent consumption, deformation and accretion of the volcanic arc or aborted marginal basin (“Mochica period”). After Cenomanian-Turonian times, the northeastward spread of the compressive strain within the South American plate caused the latter’s deformation (“Peruvian period”). The age and velocity of the subducted slab are decisive factors in the general strain regime within the subduction system; whereas variations of the convergence rate at the trench and inherited extensional structures determine the age and location of the shortlived compressiorial events. These generally correlate with plutonic gaps. Although poorly known, wrenching movements may have been important in the Cretaceous evolution of the Peruvian margin.