Paper No. 12
Presentation Time: 11:45 AM
DYNAMIC TOPOGRAPHY OF THE WESTERN GREAT PLAINS: PROPOSED SURFACE EXPRESSIONS OF MANTLE DYNAMICS IN THE RATON SECTION OF NEW MEXICO AND COLORADO
Located in New Mexico and Colorado, the Raton section of the Great Plains is a topographically-distinct province characterized by widespread volcanism and dramatic erosion in the late Cenozoic. Identifying the mechanisms that drive the evolution of this landscape remains one of the principle geologic tasks for the region and is addressed here with multiple existing datasets. Normalized channel steepness index (ksn) analysis identifies anomalously steep river slopes and has revealed a NE trend of non-equilibrium stream profiles where differential incision occurs across broad (50-100 km) convexities. 40Ar/39Ar ages of basalt-capped paleosurfaces in the Raton-Clayton and Ocate volcanic fields are used to calculate denudation rates throughout the region. We observe that rates of denudation systematically increase towards the NW in both volcanic fields—suggestive of regional tilting. An onset of more rapid denudation is also observed in the Raton-Clayton field beginning at ca. 3.6 Ma. Moreover, the gradual southeasterly slope of the Great Plains in the southern Raton section is dissected by 400-m-deep canyons and is punctuated in two places by major NE-trending erosional escarpments. These features rise 300-400 m from base-to-top and impart a staircase-like topographic profile to the region. Tomographic images from the EarthScope experiment confirm that our observed topographic patterns correspond to a significant, NE-trending velocity transition zone at the margin of the Jemez anomaly (a well-imaged zone of low velocity in the upper mantle). Given this connection, we propose that the erosional landscapes of this unique area are, in large part, the surface expression of dynamic mantle-driven uplift since at least ca. 3.6 Ma. Apatite fission-track ages that indicate a tilted geometry of the 30 Ma 110 ºC isotherm, however, suggest that mantle-driven uplift may have been initiated much earlier.