Gravity-driven large-scale deformation system in the Tumbes-Guayaquil forearc basin, Northern Andes (Northern Peru-Southern Ecuador)

The offshore Tumbes-Guayaquil forearc basin in the accretionary prism of Northern Peru-Southern Ecuador shows evidence of gravity-driven large-scale deformation systems active during the Late Neogene-Quaternary period. Subsurface data and the construction of eight structural cross-sections show that the ∼8 km-thick Oligocene-Quaternary sedimentary infill is detached seaward and completely decoupled from the underlying inner accretionary prism systems. The Corvina décollement in the Tumbes basin and the Posorja décollement in the Guayaquil basin constitute two thin-skinned gravity tectonic systems associated with kilometer-scale, updip “raft” extensional structures paired with downdip fold-thrust systems (Barracuda and Domito thrust systems). Although many previous studies have described the structural and stratigraphic architecture of the Tumbes-Guayaquil forearc basin, no model explicitly accounts for this anomalous large-scale gravity tectonics. We propose that this gravity tectonic style, more commonly observed in passive continental margins, is primarily controlled by the combination of tectonostratigraphic features, including crustal-scale transtensional deformation related to oblique convergence along the Northern Andean margin, basal décollement slope tilting, strong sediment accumulation, and the presence of overpressured shales.