Oligocene‐Miocene back‐thrusting in southern Mexico linked to the rapid subduction erosion of a large forearc block

Abstract

[1] Both the timing and mechanism for the removal of a $150-250 km wide forearc block from southern Mexico during the Cenozoic are controversial. Principal competing hypotheses are (1) removal due to sinistral strike-slip shear, in which slow, diachronous removal of the Chortis Block throughout the Cenozoic is inferred, and (2) removal due to subduction erosion, in which rapid removal of a large forearc block during the late Oligocene/early Miocene is inferred to be synchronous with the rapid landward migration of the southern Mexican arc. New data indicate northeast-directed back-thrusting in (1) the Chacalapa shear zone west of À96.5 E, with the timing of shear deformation bracketed by a 25.5 AE 0.5 Ma U/Pb zircon age and a 20.7 AE 0.6 Ma Ar/Ar biotite age, and (2) in an unnamed shear zone to the south, with the timing of deformation bracketed by a 27.5 AE 0.5 Ma U/Pb zircon age and a 25.1 AE 0.2 Ma Ar/Ar biotite age. Zircon and biotite ages date the emplacement and cooling of deformed plutons, respectively. The observed back-thrusting is consistent with a model of forearc removal due to subduction-erosion processes because it is evidence for subduction-orthogonal shortening occurring within the upper plate just before the landward migration of the southern Mexican arc. Rapid subduction of the southern Mexican forearc could have recycled continental lithosphere into the upper mantle at a rate up to half the global average rate of subduction erosion during the late Oligocene/early Miocene.

Late Cretaceous-Oligocene magmatic record in southern Mexico: The case for a temporal slab window along the evolving Caribbean-North America-Farallon triple boundary

“…The exhumation of the Xolapa metamorphic complex and the removal of the fore arc in the Guerrero‐western Oaxaca section of the SMS has been a slightly diachronic process, bracketed between 34 and 25 Ma at the longitude of Acapulco, and between 27 and 18 Ma and 25 and 21 Ma in western Oaxaca [ Ducea et al ., ; Keppie et al ., ]. The two processes have been explained by subduction erosion associated with the internal weakening of the magmatic arc and, possibly, an acceleration of the subduction velocity [ Keppie et al ., ; Keppie et al ., ]. When compared with the plate reconstruction for this time interval, it is clear that fore arc removal and exhumation of the Xolapa Complex occurred after the passage of the trailing edge of the Chortís block (Figures d and e) [ Morán‐Zenteno et al ., ; Keppie et al ., ].…”

Forearc strike-slip displacement as an alternative to subduction erosion, with examples from Mexico and California (sinistral Nacimiento fault)

“…The reader is referred to Keppie et al (2012) and Ducea and Chapman (2018) for alternative interpretations of most of the information presented earlier and discussed later in the text.…”

Exploiting individual U–Pb zircon ages and Ti-in-zircon crystallization temperature data to identify high zircon-production events in the Xolapa terrane

“…Dataset 2 consists of crystallization temperatures (CT) estimated from previously obtained zircon grains whose Ti content was acquired ( [1] , [8] , [10] , [11] ; Appendix C ) using the modified Ti-in-zircon geothermometer of [2] . Crystallization temperature (CT; x-axis) is plot versus the corresponding age of each zircon grain ( Fig.…”