Unraveling the evolution of a hanging wall using stream profile analysis: The case of the Amatlán de Cañas half–graben, northern sector of the Jalisco Block (center-west of México)

Abstract:

Rivers are key elements of the landscape highly sensitive to the changes imposed by tectonics. In zones subject to tectonic forcing rivers steepen their gradients and in the case of a rapid increase in the rate of rock uplift, rivers form a knickpoint that propagates through the fluvial network conveying information of the new base­­–level. Here we exploited the use of the stream profile analysis to unravel the tectonic evolution of the Amatlán de Cañas half–graben (ACHG), a Pio-Quaternary extensional structure with ~1500 m of relief located in the northern sector of the Jalisco Block. We found that both the normalized channel steepness index (k_sn) and relief are particularly high in the central part of the ACHG. We also identified two zones of high k_sn values in several rivers where knickpoints are propagating. Our stream profile analysis indicates that the formation of the ACHG resulted from two rock uplift pulses. Projecting the longitudinal profile of reaches located upstream of knickpoints we estimate that the uplift in ACHG exceeded 0.5 km. Although the tectonic pulses built the relief of the ACHG, the incision of the Ameca River, which flows southeasterly, seems to be rejuvenating the relief as both the high k_sn values and the distribution of knickpoints along the piedmont suggest.