Analogue model of inversion tectonics explaining the structural diversity of late cretaceous shortening in southwestern Mexico

The Laramide fold-and-thrust belt in southern Mexico is characterized by N-S-trending structures in its central and eastern part and by NW-SE-trending structures in its western part. Here, we investigate, experimentally, the possibility that the Laramide structures of southern Mexico may be the result of inversion of previously thinned lithosphere zones under oblique compression. A revision of the geology of this region shows that the presence of two extensional basins, representing relatively weak blocks within more rigid lithosphere, strongly controlled the subsequent deformation pattern. For modeling purposes, we divided the southern Mexico lithosphere into blocks with different strength profiles: (1) a stable craton; (2) a weak block composed of the Guerrero Morelos Platform; (3) a relatively strong block exposing the pre-Cretaceous Tejupilco schist and the Early Cretaceous Teloloapan volcanic arc (Tejupilco anticlinorium); and (4) a weak block represented by the Arcelia-Palmar Chico basin. A series of physical experiments simulating the mechanical response of an analogue lithosphere composed of five simplified strength profiles was constructed. The model lithosphere was thinned orthogonally and shortened obliquely. Shortening was accommodated mainly by reactivation of preexisting extensional structures. The resulting orogenic deformation in the models is not entirely sequential and foreland-progressive. Inversion tectonics of extensional basins is thus proposed as an explanation for the structural diversity observed in Late Cretaceous shortening of southwestern Mexico. The predictions of our lithospheric model may be tested when more geophysical information about the structure of the southern Mexico lithosphere becomes available.