Rheological boundary layer (RBL)
The LAB (lithosphere–asthenosphere boundary) is a rheological boundary layer (RBL). Colder temperatures at Earth’s shallower depths affect the viscosity and strength of the lithosphere. Colder material in the lithosphere resists flow while the “warmer” material in the asthenosphere contributes to its lower viscosity. The increase in temperature with increasing depth is known as the geothermal gradient and is gradual within the rheological boundary layer. In practice, the RBL is defined by the depth at which the viscosity of the mantle rocks drops below .
However, mantle material is a non-Newtonian fluid, i.e. its viscosity depends also on the rate of deformation. This means that the LAB can change its position as a result of changes in the stresses.
The LAB (lithosphere–asthenosphere boundary) is a rheological boundary layer (RBL). Colder temperatures at Earth’s shallower depths affect the viscosity and strength of the lithosphere. Colder material in the lithosphere resists flow while the “warmer” material in the asthenosphere contributes to its lower viscosity. The increase in temperature with increasing depth is known as the geothermal gradient and is gradual within the rheological boundary layer. In practice, the RBL is defined by the depth at which the viscosity of the mantle rocks drops below .
However, mantle material is a non-Newtonian fluid, i.e. its viscosity depends also on the rate of deformation. This means that the LAB can change its position as a result of changes in the stresses.