Fig. 6

Time evolution of plastic-zone depth. Maximum depth of brittle yielding over time shown for the critical experiments a, b l i d A2 and l i d A5 with depth-constant yield stress, c, d l i d B3 and l i d B7 with depth-dependent yield stress and e, f l i d C2 and l i d C5 with a composite yield stress, where there is no subduction with the free-slip surface (top row) but subduction with the free surface (bottom row). The depth of the thermal lithosphere (sampled at T=700 K and marked by a black line in Fig. 5 b, g) is indicated by the dark grey band, whereby its thickness indicates the range between the minimum and the maximum depth found at the given point in time. A sudden drop of the graph to deep levels (>200 km) indicates the initiation of subduction