Structural styles and tectonic evolution of the Santiago Basin, Peru; implications for hydrocarbon traps

The Santiago Basin of the northern Peruvian sub-Andes is a structurally complex region related to a combination of thin- and thick-skinned deformation and the impact of salt tectonics during Andean deformation. Oil shows in this basin are very common, and even though the first exploration campaigns started in the 1940s, no commercially exploitable hydrocarbons have been discovered yet. We present three basin-scale structural transects and refined structural interpretations, based on vintage 2-D seismic data and well tops that help elucidate the relationships between thin-skinned and deep-seated, thick-skinned structures. Two dip sections were kinematically restored to the top of the Yahuarango formation, one of the youngest pre-Andean units. We calculated the depth to the intra-basement detachment to be approximately 20 km (12 mi), a value that correlates with other thick-skinned detachments and earthquake hypocenters from the region. We recognized a varied inventory of salt-related structures, which we interpret to be part of the approximately 800-km (500-mi)-long Peruvian Salt Belt. The onset of salt movement occurred soon after salt deposition, likely through sediment loading. Our data suggest that Miocene-Pliocene basin deformation starting at 5.3 Ma has been sustained until the present-day. Shortening ranges from 7.31 km (4.54 mi) to 7.56 km (4.70 mi) (5.9% and 6.1%, respectively), corresponding to Miocene-Pliocene deformation rates of 1.3-1.4 mm/yr. These values are significantly lower than those of adjacent regions in the sub-Andes. This may be related to the combined effects of pressure solution, strain accommodation, or deflection by crustal-scale faults farther west.