Continental delamination and the Colorado Plateau

Abstract

Continental lithosphere is in unstable mechanical equilibrium because its mantle layer is denser than the asthenosphere. If any process such as cracking, slumping, or plume erosion initially provided an elongated conduit connecting the underlying asthenosphere with the base of the continental crust, the dense lithospheric boundary layer could peel away from the crust and sink. An analytic model for sinking velocities at the critical initial time shows that instability occurs if the effective viscosities of the lower continental crust and the rising asthenosphere are no more than 1019 P. Analogies to subduction suggest that the mature instability would grow laterally at plate tectonic velocities; however, it would be almost aseismic. Loss of the cold mantle boundary layer would cause uplift, increased heat flow, reduced seismic velocities, and perhaps emplacement of basalt flows, mantle diatremes, and granodiorite sills. A one‐dimensional thermal model of the formation of a new boundary layer predicts a half life of about 3×107 years for this thermal anomaly and uplift. As an example, the geologic and geophysical data from the Colorado Plateau are shown to be consistent with the hypothesis that it was uplifted by a delamination event 30 m.y. ago and perhaps a second event about 5 m.y. ago.

Finite frequency tomography in southeastern Tibet: Evidence for the causal relationship between mantle lithosphere delamination and the north–south trending rifts

“…[17] The thickening and deformation of the lithosphere caused by the Indo-Eurasia collision is certainly a likely geological setting for the initiation of the lithospheric delamination [Bird, 1979], though the exact mechanism for the initiation of the delamination of the mantle lithosphere is unclear. Shear heating through viscous dissipation in the lithosphere likely plays a role in weakening the lithosphere [Kincaid and Silver, 1996;Schott et al, 2000] and the initiation of the delamination at a localized shear zone.…”

More constraints to determine the seismic structure beneath the Central Andes at 21°S using teleseismic tomography analysis

“…The presence of anomalous materials in the upper mantle-lower crust region could be related to the idea of lithospheric removal or delamination, originally introduced to explain the presence of elevated plateaus, as Tibet or Altiplano-Puna (e.g., Bird, 1979;Kay and Kay, 1993). In the case of delamination, thick and cold lithosphere delaminates or separate from the base of the continental crust and sinks into the asthenosphere, process that is usually associated with uplift and mafic magmatism.…”

Origin of the Permian-Triassic Iberian Basin, central-eastern Spain

“…Similar processes took place in other segments of the Hercynian Belt (Malavielle et al, 1990 ;Se ranne, 1992 ). High relief and thick crust are stable while compression at the edges of the belt is maintained, but after its ce ssation, gravitational instability re sults in a short period of time (Bird, 1979;Houseman et al ., 1981;Glazer and Bartley, 1985). Signifi cant weakening occurs 15-20 m.y.…”