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

摘要

The causal mechanisms for the onset andnpatterns of post-Miocene erosion of the westernnGreat Plains remain the subject of annenthusiastic debate concerning the roles ofnclimatically modulated geomorphic parametersnand tectonic rock uplift as drivers ofnlong-term erosion. This study distinguishesnbetween these drivers on the plains of NewnMexico and Colorado, where post-Miocenenerosion and late Cenozoic volcanism of thenJemez lineament have produced distinctivenmodern landscapes characterized by deepnbedrock canyons and inverted, basalt-cappednmesas. The 40Ar/39Ar ages of basalt-cappednpaleosurfaces defi ne an episodic eruption historynin the Raton-Clayton and Ocate volcanicnfi elds and help to quantify patterns, amounts,nand rates of differential erosion. Several datansets indicate patterns of NE-trending geologicnfeatures that require explanation, including:n(1) crude volcanic “belts” of similar age,n(2) parallel NE-oriented erosional escarpmentsnretreating toward the NW, (3) differentialndenudation rates increasing systematicallynNW from a NE-trending hinge line of “low tonno” erosion on the Great Plains, (4) a NEtrendingnzone of broad (50–100 km) convexitiesnin stream profi les identifi ed by an analysisnof strath terraces and channel steepnessn(ksn), (5) reorganization of stream networksnthat took advantage of an apparent relativenbase-level fall in the SE, and (6) an ~150-kmlong,n40Ar/39Ar-dated composite paleo surfacenthat has been tilted 64 milli degrees/Ma sincen3.4 Ma. Our synthesis of new 40Ar/39Ar geochronologynwith new calculations of regionalnsurface denudation, channel steepness, andntilt rates shows that post-Miocene patternsnof landscape evolution are best interpreted as related to dynamic uplift along the NEtrendingnJemez lineament, with second-ordernimpacts from climate-driven geomorphicnvariables. We interpret this dynamic uplift tonbe ultimately due to changing mantle structurenand buoyancy with associated crustalnmelt fl ux.