Marton, F. C., C. R. Bina, S. Stein, and D. C. Rubie, Metastable olivine and the buoyancy and velocity of subducting slabs, Eos, Transactions of the American Geophysical Union, 79, Spring Supplement, S348, 1998.
T51B-07
The metastable persistence of olivine in a subducting slab is expected to create a low density region below the depth of the olivine to wadsleyite (beta phase) equilibrium boundary and thus a region of positive buoyancy. The vertical descent velocity of the slab, an important parameter determining the size of the metastable wedge of olivine, is presumably a function of the gravitational and buoyant forces acting on the slab, as well as the viscous drag acting on its surfaces, with the buoyant and drag forces opposing each other. The presence of a low density metastable wedge yields a positive buoyancy anomaly, thereby reducing a slab's downward velocity and the associated drag forces. A decreased descent rate, however, allows the slab to warm up, which thermally erodes the metastable wedge by enhancing the transformation kinetics. Such negative feedback mechanisms may serve to regulate lithospheric subduction rates. We examine buoyancies and terminal velocities for simple models of slabs descending through a viscous mantle, for both cases of equilibrium and metastable olivine phase transformations, to determine the net effect of the presence of a metastable wedge on subduction dynamics.
Copyright © 1998 American Geophysical Union