Landscape evolution en the San Marcos, El Madroño and Las Vigas faults, north of the triple junction of the Jalisco block, Mexico

Abstract

The landscape evolution of the region of the triple junction of the Jalisco Block is the result of Pliocene and Quaternary tectonic and volcanic processes which have produced the formation of tectonic depressions now occupied by lakes. The age of faults for this zone is not known in detail. The use of morphometric indexes. proved to be useful to detect the tectonic activity in young landscapes settings, however, few studies have used such approach to constrain the landscape evolution for west-central Mexico. In this study we analize the stream long profiles of rivers incising across the strike of the faults of San Marcos, Las Vigas and El Madroño, which are located north of the triple junction of the Jalisco Block. The morphometry of alluvial fans at the base of the fault scarps is also analyzed. The knickpoint recession age is estimated as well as the analysis of rocks (n = 6) to characterize the chemical composition of different volcanic units. The age of the zircons of the ryolithic dome of La Coronilla, which was formed over of the Madroño fault, is of 0.66 ± 0.06 ka, this allows to constrain a minimum faulting age. The results obtained here indicate that the ksn and kl indexes are the best capturing the topography resulting from the thrust produced by faults. The time when the knickpoints started to migrate occurred between 0.7 and 1 Ma. The Pliocene volcanism is calc-alcaline and the composition of lavas is between basaltic-andesite to andesite. This volcanism is different to those related to faulting which tends to be more acid (dacites and rhyolites). The agreement in age of knickpoint recession, alluvial fans and Pleistocene volcanism indicates that the landscape and the erosion at the north of the triple junction of the Jalisco Block had and important activity in the Quaternary. © 2019, Instituto de Geologã-a, Universidad Nacional Autã3noma de Mã