Home – Home – Jornals – Russian Geology and Geophysics 2014 number 7

The structure of mantle convection and spatial fields of superlithostatic pressure and vertical and horizontal stresses in the Earth’s mantle are studied in a 2D numerical model for the mantle with non-Newtonian viscosity and heat sources. The model demonstrates a jump-like motion of subduction zones and reveals abrupt changes in the stress fields depending on the stage of slab detachment. The stresses decrease dramatically in the areas without slabs. The horizontal stresses σ_xx, superlithostatic pressure, and vertical stresses σ_zz in the part of the mantle lacking intense near-vertical flows are approximately equal, varying within ±6, ±8, and ±10 MPa, respectively. However, these fields are stronger in the areas of descending slabs, where the values of the above parameters are about an order of magnitude higher (±50 MPa). This result agrees with the current views of the oceanic slabs as the most important agent of mantle convection. We have found significant differences between the σ_xx, σ_zz, and pressure fields. The pressure field reveals both the vertical and horizontal features of slabs and plumes, clearly showing their long thermal conduits with broader heads. The distributions of σ_xx are sensitive to the near-horizontal features of the flows, whereas the fields of σ_zz reveal mainly their vertical substructures. The model shows the presence of cool remnants of lithospheric slabs in the lower mantle above the thermal boundary layer. Numerous hot plumes penetrating through these high-viscosity remnants, as well as the new descending slabs, induce intense stress fields in the lower mantle, which are strongly inhomogeneous in space and time.