Tectono-Stratigraphic Insights on the Dynamics of a Complex Subduction Zone, Northern Peruvian Forearc

Abstract

Two main types of subduction are recognized around the world: accretionary and erosive. The northern Peruvian margin is a well-known example of a margin subjected to subduction erosion, but to date the along-margin variability and temporal changes in subduction process and forearc basin evolution have not been characterized in detail. Interpretation of regional seismic lines and integration of oil-industry wells and seafloor data captures the erosive nature of subduction underneath the forearc with only a minor accretionary component to the north. Episodes of uplift driven by plate coupling were followed by normal faulting/extensional collapse due to plate decoupling. This mechanism explains the dominance of normal faulting across the forearc until the Oligocene with a slight reactivation within the Miocene. The subduction history is complex and includes a reduction in plate convergence rate related to forearc crustal shortening, represented by large-scale structures including the Peru fault (reactivated) and the Illescas fault-propagation anticlines of the Northwest Peru transpressional system. This crustal deformation started in the Miocene. Integration with magnetic anomaly data indicates that activity of the present-day transpressional system driven by tectonic escape of the Nazca Sliver toward the northeast, may explain the seismicity gap in southern Ecuador and northern Peru. An evolutionary model of the northern Peruvian margin shows how subduction zone geodynamics left its erosive fingerprint in the forearc basin configuration.