Fig. 1: Temperature and viscosity fields determined by yield stress values.
From: Global mantle convection models produce transform offsets along divergent plate boundaries
Thermal field (first column) and viscosity field (remaining columns) variation in response to yield stress values. Rows a–e show snapshots from four time-dependent calculations (rows c, d are from the same calculation). In columns 2–4 different viewing angles are shown (the different columns) for the time corresponding to the first column. Rotation of the spheres in columns 3 and 4 is around the north-south axis defined by the viewing angle of the second column and is through an angle of approximately Ï•. Asterisks on specific viscosity field panels indicate that the viewing angle in that column corresponds to the position used to render the temperature field in the first column. In a the non-dimensional surface yield stress is 2 × 106 (11 MPa) and increases linearly over the top 2% of the mantle thickness to a value of 2 × 107 (110 MPa). In b the non-dimensional surface yield stress is 1.5 × 107 (85 MPa) and increases linearly over the top 2% of the mantle thickness to a value of 2 × 107 (110 MPa). In c, d the surface yield stress is uniform with depth with a value of 2 × 107 (110 MPa). Panel d is from the same calculation as row (c) but at a time 350 Myr later. In e the yield stress is uniform with depth with a value of 3 × 107 (160 MPa). The panel in the green box is the viscosity field shown in (e) viewed from over the north pole. The cyan horizontal line indicates where the sphere would be sliced in order to obtain the thermal field image in the first column of (e). The thermal isosurfaces in the first column have a non-dimensional super-adiabatic temperature of 0.85. The viscosity fields are depicted 12 km below the surface of the 2890 km deep mantle. Black and red arrows annotate features described in the text. Colour bars corresponding to the superadiabatic temperature and the viscosity fields are located at the bottom of the figure. The scale on the viscosity colour bar shows multiplicative factors for the reference viscosity 4.5 × 1019 Pa ⋅ s. The scale for the temperature fields is in fractions of the core-mantle-boundary temperature, 2500 °C.
