Mantle-driven dynamic uplift of the Rocky Mountains and Colorado Plateau and its surface response: Toward a unified hypothesis

Abstract

The correspondence between seismic velocity anomalies in the crust and mantle and the differential incision of the continental-scale Colorado River system suggests that signifi cant mantle-to-surface interactions can take place deep within continental interiors. The Colorado Rocky Mountain region exhibits low-seismic-velocity crust and mantle associated with atypically high (and rough) topography, steep normalized river segments, and areas of greatest differential river incision. Thermochronologic and geologic data show that regional exhumation accelerated starting ca. 6-10 Ma, especially in regions underlain by low-velocity mantle. Integration and synthesis of diverse geologic and geophysical data sets support the provocative hypothesis that Neogene mantle convection has driven long-wavelength surface deformation and tilting over the past 10 Ma. Attendant surface uplift on the order of 500-1000 m may account for ~25%-50% of the current elevation of the region, with the rest achieved during Laramide and mid-Tertiary uplift episodes. This hypothesis highlights the importance of continued multidisciplinary tests of the nature and magnitude of surface responses to mantle dynamics in intraplate settings.

Relation between alternations of uplift and subsidence revealed by Late Cenozoic fluvial sequences and physical properties of the continental crust

“…Excluding sites in the vicinity of recent drainage diversions (Donahue et al, 2013), there is no reason why incision within this system should not serve as a proxy for uplift since the modern geometry of the Colorado catchment came into being at ~6 Ma . Contrary to other recent studies (Karlstrom et al, 2012;Donahue et al, 2013), which have inferred constant fluvial incision rates for multimillion-year timescales in this region, we identify variable rates that correlate with the expected climatic forcing (see also below).…”

“…7) at nearby sites (Karlstrom et al, 2012). We thus infer that the highest terrace recognized dates from MIS 22 or thereabouts.…”

“…Durrheim & Mooney, 1994;Karlstrom et _ al., 2002). More recent studies (e.g., Gilbert & Sheehan, 2004;Karlstrom et _ al., 2012) Decker, 1995, andDecker et al, 1988) but without explaining the revision; on this basis a slightly thicker mobile lower-crustal layer would be predicted. We are not aware of any measurement of the heat production in this particular borehole; however the value adopted is similar to others measured in the surrounding region (e.g., Edwards et al, 1978) and the resulting basal heat flow is within the ~34±4 mW m -2 range long considered characteristic of the Great Plains (e.g., Roy et al, 1968;Decker & Smithson, 1975).…”

“…This composite transverse profile sought to integrate data from sites (up to ~250 km apart) adjoining both the main Colorado River and its tributary, the Gunnison; however, it is now clear (Karlstrom et al, 2012;Donahue et al, 2013) that rates of fluvial incision vary significantly across this substantial region. In the vicinity of Grand Junction the disposition of the dated Grand Mesa basalt indicates ~1500 m of incision since ~10 Ma at a time-averaged rate of ~0.15 mm a -1 (Karlstrom et al, 2012).…”

“…Nearby river terrace deposits ~100 m above the modern valley floor, in which tephra from the ~600 ka Yellowstone eruption is preserved, indicate a similar incision rate; it has thus been argued on the basis of this sparse evidence that the incision rate has remained constant for ten million years (Karlstrom et al, 2012;Donahue et al, 2013).…”