Figure 4
From: Depletion of the upper mantle by convergent tectonics in the Early Earth
Formation of an accretionary V-shaped terrain and over-thickened melt-depleted mantle during two-sided subduction at constant convergence velocity of 5 cm/year and elevated mantle temperature ΔT = 250 °C (Tp = 1550 °C). (a) Flat ocean–ocean subduction with highly depleted mantle (4.7 myrs from the beginning of the experiment). Eclogitization of the subducting oceanic crust (density ≥ 3450 kg/m3) occurs at ~ 150 km depth. (b) Two-sided vertical subduction with V-shaped accretionary terrain atop over-thickened depleted mantle under the left-hand plate (23.4 Myr from the beginning of the experiment). Note the reverse viscous flow of the depleted mantle detached from the left-hand slab. Eclogitization of the subducting oceanic crust (density ≥ 3450 kg/m3) occurs at ~ 250 km depth. (c) Large V-shaped accretionary terrain and voluminous stagnant slabs in the mantle transition zone (38.8 Myr from the beginning of the experiment). Density and effective viscosity fields with velocity vectors are shown for each stage as separate panels at the bottom right and at the top right, respectively. Dotted dark-blue lines in b and c of the left column indicate upper and lower boundaries of the mantle transition zone. Arrows show direction of plate motion (not to scale) and viscous flow of the depleted mantle. The colour key is as in Fig. 2. Viscosity of the mantle is intrinsically dependent on pressure, temperature, degree of depletion and presence of fluid/melt (see “Method”). The rheological transition between the rigid lithospheric and low-viscosity asthenospheric (sublithospheric) mantle approximately corresponds to the 1300 °C isotherm. Prescribed velocity of the left-hand plate is 5 cm/year.
