Subcontinental sinking slab remnants in a spherical geometry mantle model

Comparisons of the paleogeographic record with seismic tomography sections from the mantle below Asia indicate that detached slab remnants associated with a range of ages since subduction spanning roughly 100 Myr appear to occupy mid-mantle depths at different sites. More than one explanation for the observed spectrum of ages at similar depths may be plausible. To identify key parameters controlling the sinking rate of a slab, we examine the effects of mantle viscosity, Rayleigh number, and spherical geometry, as well as the role of slab properties, such as strike width, depth extent at the time of slab detachment, and slab rheology. We model scenarios featuring detached mantle slabs in 3-D calculations and conclude that the initial depth extent of a subducted slab segment is a key parameter determining the rate at which the slab sinks. We estimate that stiff slabs are able to occupy mid-mantle depths for ages ranging from approximately 35 to 150 Myr, depending on the initial depth extent of the slab at the time of its detachment from the lithosphere. This age range results from the time that different slab fragments require to cross the viscosity interface at the upper mantle/lower mantle boundary. In cases featuring mature slabs where the lower section of the slab has penetrated the lower mantle prior to detachment, entrainment by the deep sinking segment helps the young upper mantle section of the slab cross into the lower mantle much more quickly than a slab segment initially confined to the upper mantle.