A. Manglik et Ur. Christensen, EFFECT OF MANTLE DEPLETION BUOYANCY ON PLUME FLOW AND MELTING BENEATHA STATIONARY PLATE, J GEO R-SOL, 102(B3), 1997, pp. 5019-5028
We analyze a dynamical model of plume-lithosphere interaction in two-d
imensional Cartesian geometry that takes into account the buoyancy of
the depleted residue produced by melt extraction. The plume enters thr
ough the open bottom boundary at 400 km depth and leaves through the r
ight side boundary of the model box. The viscosity is strongly pressur
e and temperature dependent. We use a large number of Lagrangian trace
r particles to monitor progressive melting in the plume head and to tr
ack the advection of the depleted residue. The density reduction in th
e residue enhances small-scale instabilities sinking from the bottom o
f the lithosphere into the depleted layer. Initially, the melt product
ion rate is slightly enhanced when depletion buoyancy is taken into ac
count. However, in the subsequent evolution, melt production rates are
lowered by a factor in the range 0.5 - 0.65, depending on the initial
thickness of the lithosphere, compared to cases without density diffe
rence of the residue. The buoyancy of the residual mantle opposes its
advection away from the top of the plume. A depleted root is formed at
the bottom of the lithosphere, which inhibits further thermal erosion
of the plate. It forces the plume flow to stagnate at greater depth a
nd hence reduces the melt production rate. The effect is particularly
strong for a case where the plume rises beneath locally stretched lith
osphere. The results are compared to the evolution of volcanism at the
Cape Verde hotspot and the Kenya rift.