RIVERS RESPONSE TO TECTONICS IN EXTENSIONAL LANDSCAPES: A CASE OF STUDY IN THE JALISCO BLOCK (WEST-CENTRAL MEXICO) AND ADJACENT AREAS

Rivers are key elements of the landscape that capture changes in tectonic and/or climatic conditions. Many studies have used morphometric indexes of rivers to assess the tectonic forcing of landscape; however, the case for the response of rivers in extensional settings where volcanic activity has covered vast areas of the landscape has remained poorly documented. We evaluate the case of west-central Mexico where landscape results from an extensional tectonic regime initiated in the Miocene and continuing to the present, and where there is a marked volcanic activity of Eocene-Oligocene and Pliocene-Pleistocene age. We use the normalized channel steepness index (k_sn) and compare this with other morphometric parameters such as the hillslope gradient, hillslope convexity, hillslope concavity, terrain rugosity and first order streams gradient (Fosg). Regressions of morphometric parameters as a function of k_sn index have R² greater in the Eocene-Oligocene volcanic landscapes (51% to 57%) in comparison to the Pliocene-Pleistocene volcanic landscapes (39% to 49%). The scaling between the hillslope concavity and k_sn is the best among all the models tested, meaning that the incisional response dominates over the landscape. Tukey’s test show that the distribution of the concavity and the k_sn index is not significantly different (p >0.05) among volcanic landscapes. The ANCOVA analysis also indicates that both concavity and rugosity are not significantly different among volcanic landscapes (p >0.05). Tukey’s test and the ANCOVA analysis also show that the distribution Fosg does not significantly differs among extensional landscapes (p >0.05). Our results indicate that even though volcanism might inhibit the response of rivers to tectonics, given the supply of large volumes of rock and sediment into the landscape, river incision is still mostly controlled by tectonic activity.