The structure of mantle flows and stress fields in a two-dimensional convection model with non-Newtonian viscosity

Abstract

Abstract 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 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 σxx, superlithostatic pressure, and vertical stresses σzz 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 among the σxx, σzz, 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 σxx are sensitive to the near-horizontal parts of the flows, whereas the σzz fields reveal mainly their vertical substructures. The model shows the presence of relatively cold remnants of 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.