A Review on Tectonic Record of Strain Buildup and Stress Release across the Andean Forearc along the Gulf of Guayaquil-Tumbes Basin (GGTB) near Ecuador-Peru Border

Abstract

Gravimetric and geologic data show that the reactivation of the Neogene Interandean depression and/or the ~75 -65 Ma ophiolite suture into the modern dynamic of the Andes controlled the Gulf of Guayaquil Tumbes basin (GGTB) location and evolution during the past 1.8 -1.6 Myr at least. Depending on whether the remobilization occurred along the interandean depression or the ophiolite suture, the GGTB evolved trough pure or simple shear mechanisms, respectively. Because the GGTB exhibits an along strike tectonic asymmetry associated with a pervasive seismic gap, the simple shear solution is more likely. Tectonic inversion occurred along a mid-crust detachment (the Mid-Crust detachment hereafter) matching the ophiolite suture that accommodates the North Andean Block (NAB) northward drift. The so-called Decoupling Strip located at the shelf slope break accommodated the tensional stress rotation from N-S along the shelf area i.e. NAB-drift induced to E-W along the continental margin i.e. subduction-erosion-induced. The landward dipping Woollard detachment system located at the Upper-Lower slope boundary connects the subduction channel at depth, allowing the Upper slope to evolve independently from the Lower slope wedge. The long-term recurrence interval between earthquakes, the strong interplate coupling, and the aseismic creeping deformation acting along the main low-angle detachments i.e. the Woollard and the Mid-Crust detachments may account for the pervasive seismic gap at the GGTB area. Because the subduction channel exhibits no record of significant seismic activity, no evidence exists to establish a link between the GGTB sustained subsidence and a basin-centered asperity. Because the GGTB is a promising site of hydrocarbon resources, to understand processes at the origin of this escape-induced forearc basin has a major economic interest.

A new view for the geodynamics of Ecuador: Implication in seismogenic source definition and seismic hazard assessment

“…The black continuous lines are main crustal fault systems shown in Figure . Discontinued lines in the Gulf of Guayaquil area are detachments from Bourgois []. Pentagons represent historical epicenters relocated by Beauval et al [].…”

“…The origin and precise depth distribution of the cluster is not yet resolved. These large events could have ruptured the subduction megathrust [ Suarez et al ., ] or continental slope detachments in the Gulf of Guayaquil [ Bourgois , ], although von Huene et al [] and Bourgois et al [] favor a rotational landslide origin for similar detachments identified south of Talara without the release of M w ≥ 7 equivalent seismic energy.…”

“…They consider that the strike‐slip fault system identified at the Gulf (Puná fault system) does not connect directly to the faults forming part of the North Andean Block southeastern frontier at present (the CCPP fault system). For Bourgois the NAB southern boundary is found along the southern edge of the gulf related to a detachment system—the Tumbes‐Zorritos detachment—and a N–S decoupling strip [ Bourgois , , Figure 5] identified at the continental slope–continental shelf break. The detachment structures bounding the decoupling strip may not be capable of generating major seismic events since the strip exhibits extensive diapiric structures that are not able to store elastic deformation.…”

“…The detachment structures bounding the decoupling strip may not be capable of generating major seismic events since the strip exhibits extensive diapiric structures that are not able to store elastic deformation. To the contrary, the Tumbes‐Zorritos detachment, in conjunction with a low‐angle midcrust creeping detachment, would be accommodating the NAB northeastward movement [ Bourgois , ] and is not ruled out as source of the 1953 M w 7.6 earthquake. For this reason the Tumbes‐Zorritos detachment is included in the NAB‐4 source zone (Figure ).…”

“…Bourgois and collaborators have extensively studied the Gulf of Guayaquil structure and evolution [Witt et al, 2006;Bourgois et al, 2007;Witt and Bourgois, 2010;Bourgois, 2013]. They describe the tectonic activity from 140 ka to the present as being restricted to normal faults bounding subsiding basins in the Gulf and to strike-slip faults connecting the detachments responsible for the basin subsidence [e.g., Witt et al, 2006].…”