Drip vs. Delamination: Are They Predictable Through Surface Observables?
Abstract
In a number of disparate geological regions, it has been postulated that the mantle lithosphere (sub-crustal lithosphere) has been thinned or completely removed. Two of the primary removal mechanisms that have been put forward include: a) delamination--a wholesale peeling away of a coherent block of the mantle lithosphere; and b) lithospheric "dripping"--viscous Rayleigh-Taylor instability of the mantle lithosphere. At locales such as the southern Sierra Nevadas and Alboran Sea/Rif-Betic-Atlas Mountains, both of these processes have been invoked. Consequently there is still significant debate as to the fundamental style of the plate behaviour. We propose that several surface (or near-surface) observables such as the surface topography, surface heat flow and P-T history of crustal rocks may be diagnostic of the removal mechanism. We test this hypothesis using 2-D numerical and 3-D scaled physical analogue modeling. We configured the models with a buoyant crust, dense mantle-lithosphere, and athenospheric mantle and using different assumed intial conditions to trigger both types of mantle lithosphere removal events. Delamination drives contemporaneous subsidence and uplift but with a distinct asymmetry, whereas mantle drip produces a more symmetrical pattern of surface topography. Calculations of the maximum temperatures at the base of the crust indicate that there is at least ~600°C increase during a delamination event due to asthenospheric replacement of mantle lithosphere. On the other hand, dripping mantle lithosphere may show a very modest increase in Moho temperature, but this depends on how much mantle lithosphere is removed. The P-T histories at lower, middle and upper crustal levels for both types of mantle lithosphere removal mechanisms show counterclockwise P- T-t paths. For the middle and upper crust, peak temperatures and peak pressures of the delamination models` are at least 0.5 kbar and 10°C higher than that of lithospheric dripping model.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.H21E1421G
- Keywords:
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- 1625 Geomorphology and weathering (0790;
- 1824;
- 1825;
- 1826;
- 1886);
- 8120 Dynamics of lithosphere and mantle: general (1213);
- 8175 Tectonics and landscape evolution