Landscape evolution of the graben of Puerto Vallarta (west-central Mexico) using the analysis of landforms and stream long profiles

摘要

The analysis of landforms and stream long profiles are useful tools that can provide information about the tectonic activity in the landscape. The west-central portion of Mexico is a region that is mostly dominated by an extensional tectonics initiated in the Miocene and continuing in the Quaternary, where there has also been a vast emission of volcanic products. Of particular importance is the graben of Puerto Vallarta which was formed during the extensional activity that opened the Gulf of California in the Miocene. Nevertheless, the geomorphology and landscape evolution of this structure has not been studied in detail. Here I present a study of the rivers, landforms and topography of Puerto Vallarta graben in order to assess its evolution, focusing on the evidences of its initial phase of formation. The geomorphological map elaborated in this study reveals the presence of lava flows and volcanic structures in the eastern sector of the graben. Here it is proposed that this volcanism occurred during the formation of the graben in the Miocene, nevertheless, radiometric dating of lavas is still required to determine the precise timing of this event. Analysis of stream long profiles confirms that knickpoints are propagating in the fluvial network at a rate of similar to 0.07 to similar to 0.7 mm yr(-1) and these were probably triggered by a drop in the base-level of rivers during the graben formation. The rates of knickpoint retreat in the graben of Puerto Vallarta are slightly lower than those observed in other recent (Quaternary) tectonic areas, however, the migration rates of the graben of Puerto Vallarta were probably higher at the onset of the faulting. Here the analysis of landforms and stream long profiles were useful to elucidate one part of the evolution of the graben of Puerto Vallarta. This study emphasizes the importance of incorporating the tectonic geomorphology in future studies of the extensional zones of west-central Mexico. (C) 2016 Elsevier Ltd. All rights reserved.