Tectonic evolution of the Tehuantepec Ridge

The Tehuantepec Ridge is one of the most prominent lithospheric structures of the Cocos Plate, yet its tectonic evolution hasremained poorly constrained until now. Calculated ocean floor ages and spreading rates, morphostructural analysis of the ridgeand the surrounding ocean floor are used to infer the tectonic evolution and pattern of the Tehuantepec Ridge and associatedstructures. The ocean floor age estimates south of the Tehuantepec Ridge suggest an age of ~26 Ma at the Middle Americatrench. A mean age difference across the Tehuantepec Ridge of ~7 Ma suggests that the Tehuantepec Ridge would be formed asa long transform fault on the Guadalupe plate, prior to 15 Ma.The full-spreading rate estimates show that there might be a differential full-spreading rate across the transform faultbetween 15 and 5 Ma, when the oceanic plate just south of Clipperton Fracture Zone was decelerating between 15 and 10 Ma,then accelerating for the next 5 Ma. We propose a model in which between 13 and 8 Ma temporarily transpressionalintratransform-spreading centers would have been existing as a consequence of the East Pacific Rise onset with an angle of~108clockwise with respect to the ceased Mathematician ridge. Our model estimates indicate that between 21 and 15 Ma aprominent pseudofault was formed south of the Tehuantepec Ridge due to an unstable offset on the Mathematician ridge thatmigrated northward. The Tehuantepec Ridge and the pseudofault trace bound a deeper oceanic basin than the surrounding area,with no corresponding anomalous depth on the western side of the East Pacific Rise. The complete absence of a pseudofaulttrace and a deeper oceanic basin on the western side of the East Pacific Rise, as well as the spreading rate changes, suggest theexistence of a microplate embedded into the Cocos Plate just south of the Tehuantepec Ridge. Also, the asymmetric and sharpmorphology of the Tehuantepec Ridge suggests that it may be the expression of a major transpressional structure along theformer transform fault on the Guadalupe plate 15–20 Ma ago