Complex deformation recorded in the western sector of the Cretaceous Arperos Basin. Late Cretaceous-Paleocene Mexican Orogen, central Mexico.

The Mexican Orogen is the most important tectonic event recorded during the Late Cretaceous-Paleocene in Mexico. This orogen conforms to the majority of the Mexican territory, and its origin is probably related to the subduction dynamics in the western margin of the North American plate. Many studies had concentrated their efforts in the foreland fold-thrus belt toward the eastern part of Mexico. However, the geometry, kinematic, and amount of shortening to the hinterland part of the orogen are unknown. Additionally, the age and kinematics of the shortening structures associated with the inversion of the early Cretaceous Arperos basin, now in the hinterland part, remains an enigma. In this work, we present a detailed structural analysis of the shortening structures and U-Pb detrital zircon ages of sedimentary rocks located in the western-central part of Mexico, with the proposal to know the main features of the contractional deformation and resolve the enigma about the Arperos basin inversion during the Mexican Orogen. The rocks of the western sector of the Arperos basin are composed of a sequence of volcaniclastic sandstone interbedded with shale and thin layers of limestone with a maximum depositional age of 133.3 ±1.1 to 110.27±0.77 Ma. This sequence is unconformably covered by a synorogenic turbidite package with a maximum depositional age of 101 ±1 Ma. All these rocks are strongly deformed by folding with a pervasive sub-horizontal axial plane cleavage and 70% shortening. Although, the Arperos basin rocks record a less pervasive second cleavage. The mesoscopic folds are asymmetric with a subhorizontal axial plane, and are class 1C, 3, and 2 based on Ramsay's classification. There is a second fold generation in the rocks of Arperos basin that refolds the firs folds. The refolded folds are type-3 mainly. The reverse faults dip 30–60° to the NE and SW, having displacements of tens of centimeters and are penetrative on the scale of tens of meters.

The data obtained in this work suggest that the hinterland part of the Mexican Orogen is represented by sedimentary rocks of Arperos Basin and synorogenic turbidites. These rocks were folded and thrusted during the late Cretaceous when the Arperos basin closed. Their complex deformation can be explained by a progressive deformation accommodated during the development of orogen.