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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS012 Oral Presentation 2200
Numerical Models of the Fate of Detached Slabs
Prof. Gary Jarvis
Earth and Space Science,York University, Toronto IASPEI, Canadian Geophysical Union
IASPEI
Julian P. Lowman, Hosein Shahnas
We examine the rate of sinking of subducted slabs in a series of idealized three-dimensional and twodimensional
simulations using a 3D Cartesian plane-layer model, and a 2D cylindrical-shell model, of
mantle convection. Our goal is to account for the inference from seismic tomographic studies that some
slab remnants have persisted at mid-mantle depths for 150 My or more while others have descended to
the base of the mantle, in much less time, where they have spread laterally for great distances along
the core-mantle boundary. We consider the influence of initial slab dimensions, viscosity stratification,
slab dip angle, mineral phase transitionsand three dimensionality on the time required to clear the
upper half of the mantle of all thermal traces of an initial upper mantle subduction zone. We find that
upper mantle slabs will persist in the upper 1500 km of the mantle for times in excess of 150 My if there
is a viscosity jump by a factor of 30 or more at a depth of 670 km. In contrast, if the initial slab
structure reaches deep into the lower mantle, it will draw all of the upper portions of the slab into the
lower half of the mantle in less than 150 My, unless the viscosity increases in the lower mantle by a
factor of 300 or more. We find that sinking rates of slab remnantsare relatively insensitive to the
presence of phase transitions when the viscosity increase at 660 km is sufficiently large. The age of slab
remnants depends most strongly onthe viscosity stratification and the total depth extent of the original
slab.
Keywords: truncated, slab, models