EVALUATING A HYPOTHESIS FOR MANTLE-DRIVEN EPEIROGENIC UPLIFT ALONG THE JEMEZ LINEAMENT OF NORTHEASTERN NEW MEXICO USING RIVER TERRACES AND LONG PROFILE ANALYSIS

We test the hypothesis that Quaternary epeirogenic surface uplift may be recorded by the terraces and long profiles of rivers that drain the southeastern Rocky Mountains. Past researchers have explained the unique geometry of terraces and basalt-capped surfaces along a ~100 km stretch of the Canadian River in northeastern New Mexico by implicating mantle-driven uplift above low velocity regions coincident with the Jemez volcanic lineament (JVL). Incision rate patterns are thought to be equal and opposite to the rate of surface uplift on the High Plains just east of the Rio Grande rift. To test this model on a more regional scale, longitudinal profiles of other major drainages in northern New Mexico were constructed from 7.5 minute topographic maps and through DEM analysis. Bedrock lithologies and the geometry of elevated terraces and basalt-capped surfaces were compiled for each river. There are a striking number of reaches that exhibit sharp knick points and/or convexities in their profiles. While some of these features seem to be bedrock-controlled, many show no indication of bedrock influence on gradient or convexity and are interpreted to be transient incision signals due to tectonism. In map view, DEM analysis suggests a possible regional spatial correlation between the appearance of multiple convexities in numerous drainages and the JVL. Preliminary analysis shows good correlations between: (1) high gradient reaches (normalized for discharge), (2) regions of highest topographic roughness, (3) rivers with highest incision rates, and (4) zones of lowest mantle velocity. Continued dating and correlation of terraces will test the model for mantle-driven epeirogenic surface uplift localized along the JVL and help constrain the timing and magnitude of that uplift.