Hypothesis for epeirogenic uplift above the Jemez lineament: Is Neogene doming recorded by river profiles and terraces?

Rivers in the Rio Grande drainage of southern Colorado and northern New Mexico drain the southern Rockies southwards through the Rio Grande rift and across the NE trending Jemez lineament. We test the hypothesis that Quaternary tectonism (both faulting and broad doming due to magmatism and mantle driven dynamic uplift) may be recorded by drainage patterns and river profiles. These effects are not easy to distinguish from those of base level fall, drainage reorganization, and climate changes, but a regional look at New Mexico's rivers through time may help distinguish tectonic from climatic and geomorphic forcings. Longitudinal profiles of major drainages in northern New Mexico were constructed from 7.5 minute topographic maps, and DEM analysis. Bedrock lithologies, geometry of elevated terrace, and positions of basalt flows were compiled for each river. There are a striking number of reaches that exhibit sharp knickpoints and/or convexities in the profile. Some of these convexities and knickpoints seem to be bedrock-controlled; that is, they exist at hard rock-soft rock contacts. However, some convexities are not controlled by bedrock (e.g. entirely in shale); and similarly, some hard rock areas show no convexity, suggesting that bedrock control cannot always be used to explain convexities. The Rio Grande exhibits a double concave profile suggesting ongoing adjustments to neotectonic and geomorphic forcings. In map pattern, DEM analysis suggests a regional spatial correlation between the appearance of multiple convexities in numerous drainages and the Jemez lineament, a northeast trending zone of Quaternary magmatism and tectonism. Slope-area analysis, combined with Hack index analysis and topographic roughness analysis show good correlations of topographic parameters: 1) high gradient reaches (normalized for discharge), 2) regions of highest topographic roughness, and 3) zones of lowest mantle velocity. Thus, we support and expand the hypothesis that convexities in drainages crossing the Jemez lineament are the result of the drainages" response to Neogene (last 6 Ma) epeirogenic warping. These further tests of the interactions of tectonics and river incision can lead to fundamental insights about neotectonics in the Rocky Mountains and Rio Grand rift as well as processes of river incision.