Dynamic topography of the western Great Plains: Geomorphic and 40Ar/39Ar evidence for mantle-driven uplift associated with the Jemez lineament of NE New Mexico and SE Colorado

Abstract

The causal mechanisms for the onset and patterns of post-Miocene erosion of the western Great Plains remain the subject of an enthusiastic debate concerning the roles of climatically modulated geomorphic parameters and tectonic rock uplift as drivers of long-term erosion. This study distinguishes between these drivers on the plains of New Mexico and Colorado, where post-Miocene erosion and late Cenozoic volcanism of the Jemez lineament have produced distinctive modern landscapes characterized by deep bedrock canyons and inverted, basalt-capped mesas. The 40Ar/39Ar ages of basalt-capped paleosurfaces define an episodic eruption history in the Raton-Clayton and Ocate volcanic fields and help to quantify patterns, amounts, and rates of differential erosion. Several data sets indicate patterns of NE-trending geologic features that require explanation, including: (1) crude volcanic “belts” of similar age, (2) parallel NE-oriented erosional escarpments retreating toward the NW, (3) differential denudation rates increasing systematically NW from a NE-trending hinge line of “low to no” erosion on the Great Plains, (4) a NE-trending zone of broad (50–100 km) convexities in stream profiles identified by an analysis of strath terraces and channel steepness (ksn), (5) reorganization of stream networks that took advantage of an apparent relative base-level fall in the SE, and (6) an ∼150-km-long, 40Ar/39Ar-dated composite paleosurface that has been tilted 64 millidegrees/Ma since 3.4 Ma. Our synthesis of new 40Ar/39Ar geochronology with new calculations of regional surface denudation, channel steepness, and tilt rates shows that post-Miocene patterns of landscape evolution are best interpreted as related to dynamic uplift along the NE-trending Jemez lineament, with second-order impacts from climate-driven geomorphic variables. We interpret this dynamic uplift to be ultimately due to changing mantle structure and buoyancy with associated crustal melt flux.