Continuing Colorado plateau uplift by delamination-style convective lithospheric downwelling

Abstract

The Colorado plateau is a large, tectonically intact, physiographic province in the southwestern North American Cordillera that stands at ∼1,800-2,000 m elevation and has long been thought to be in isostatic equilibrium. The origin of these high elevations is unclear because unlike the surrounding provinces, which have undergone significant Cretaceous-Palaeogene compressional deformation followed by Neogene extensional deformation, the Colorado plateau is largely internally undeformed. Here we combine new seismic tomography and receiver function images to resolve a vertical high-seismic-velocity anomaly beneath the west-central plateau that extends more than 200 km in depth. The upper surface of this anomaly is seismically defined by a dipping interface extending from the lower crust to depths of 70-90 km. The base of the continental crust above the anomaly has a similar shape, with an elevated Moho. We interpret these seismic structures as a continuing regional, delamination-style foundering of lower crust and continental lithosphere. This implies that Pliocene (2.6-5.3 Myr ago) uplift of the plateau and the magmatism on its margins are intimately tied to continuing deep lithospheric processes. Petrologic and geochemical observations indicate that late Cretaceous-Palaeogene (∼90-40 Myr ago) low-angle subduction hydrated and probably weakened much of the Proterozoic tectospheric mantle beneath the Colorado plateau. We suggest that mid-Cenozoic (∼35-25 Myr ago) to Recent magmatic infiltration subsequently imparted negative compositional buoyancy to the base and sides of the Colorado plateau upper mantle, triggering downwelling. The patterns of magmatic activity suggest that previous such events have progressively removed the Colorado plateau lithosphere inward from its margins, and have driven uplift. Using Grand Canyon incision rates and Pliocene basaltic volcanism patterns, we suggest that this particular event has been active over the past ∼6 Myr.

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

“…Diverse explanations have likewise been proposed for the Late Cenozoic uplift of the Colorado Plateau and the resulting incision by the Colorado River, including the development of the Grand Canyon (the online supplement of Levander et _ al., 2011, provides a list; see , for a recent review; see also below).…”

“…For instance , Granger et _ al. (2001) suggested that the alternation of base-level lowering and rising, evident in Moucha et _ al., 2009) or rebound following removal of part of the mantle lithosphere (e.g., Spencer, 1996;Levander et _ al., 2011).…”

Geometry of the Pamir‐Hindu Kush intermediate‐depth earthquake zone from local seismic data

“…It is not clear whether a Rayleigh-Taylor instability, which is a ductile process, would be capable of creating any seismicity at all. Indeed, well-constrained mantle downwellings beneath Tibet [Tilmann et al, 2003], the Andes [Schurr et al, 2006], the Colorado plateau [Levander et al, 2011], and the Sierra Nevada [Zandt et al, 2004] take place aseismically. Lorinczi and Houseman [2009] could reproduce strain rates measured for the Vrancea intermediate-depth seismic zone by numerically simulating a narrow lithospheric downwelling.…”

Constraints on the paleogeographic evolution of the North China Craton during the Late Triassic–Jurassic

“…An extensive uplift event should occur if large-scale delamination occurred (Kay and Kay, 1993;Gao et al, 2004). For example, foundering of lower crust and continental lithosphere has been claimed as a possible mechanism for the elevation of the Colorado Plateau (Levander et al, 2011). If the delamination of the eastern NCC took place in the Late Jurassic or Early Cretaceous (Wu et al, 2003a), an elevation in the eastern NCC would occur at that time, which is inconsistent with the paleogeographic evolution of the eastern NCC in the Mesozoic (Zhu et al, 2012;Li et al, 2013).…”