Abstract

Trench-parallel extensional strain resulting from the northward drift of the North Andean block has controlled the tectonic evolution of the Gulf of Guayaquil-Tumbes Basin, at least for the past ∼1.8–1.6 Ma. Industrial multichannel seismic and well data document that E-W to ENE, low-angle detachment normal faults, the Posorja and Jambelí detachment systems to the north and the Tumbes detachment system to the south, accommodated the main subsidence step along the shelf area during late Pliocene-Quaternary times (1.8–1.6 Ma to present). Two tectonic regimes showing different styles and ages controlled the evolution of the southern Ecuador and northern Peru continental margin and shelf. The ∼N-S extensional regime along the shelf area is related to North Andean block drift, whereas the E-W extensional regime along the continental margin results from tectonic erosion at depth. Strain rotation takes place along a major N-S–trending transfer system formed by the Inner Domito fault and the Inner Banco Peru fault, which bound the detachment systems to the west. The strike-slip component along this transfer system, roughly located at the continental margin-shelf break, evolved as a response to slip along the detachment systems bounding the basin to the north and to the south. The Tumbes detachment system is the master fault controlling basin evolution through time, and it may represent the shallower expression of a reactivated obduction megathrust. It connects landward with the continental structures assumed to be part of the eastern frontier of the North Andean block. For the past ∼2 Ma, the total lengthening calculated along a complete N-S transect of the Gulf of Guayaquil-Tumbes Basin ranges between 13.5 and 20 km. This lengthening is compatible with the documented drift of the North Andean block for the same period of time. The Gulf of Guayaquil-Tumbes Basin is not a classical pull-apart basin; it exemplifies a particular type of pull-apart basin basically controlled by (1) detachments extending downward across the brittle crust, and (2) plate coupling along the subduction décollement, which controls the inward segmentation of deformation.

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