Oceanic spreading ridges exhibit structural changes as a function of spreading rate, mantle temperature and the balance of tectonic and magmatic accretion. The role that these or other processes have in governing the overall shape of oceanic ridges is unclear. Here, we use laboratory experiments to simulate ridge spreading in colloidal aqueous dispersions whose rheology evolves from purely viscous to elastic and brittle when placed in contact with a saline water solution. We find that ridge shape becomes increasingly linear with spreading rate until reaching a minimum tortuosity. This behaviour is predicted by the axial failure parameter Π_F, a dimensionless number describing the balance of brittle and plastic failure of axial lithosphere. Slow-spreading, fault-dominated and fast-spreading, fluid intrusion-dominated ridges on Earth and in the laboratory are separated by the same critical Π_F value, suggesting that the axial failure mode governs ridge geometry. Values of Π_F can also be calculated for different mantle temperatures and applied to other planets or the early Earth. For higher mantle temperatures during the Archaean, our results preclude the predicted formation of large tectonic plates at high spreading velocity.

海洋扩张脊表现出结构变化，这是扩张速度，地幔温度以及构造和岩浆增生平衡的函数。这些或其他过程在控制洋脊整体形状中的作用尚不清楚。在这里，我们使用实验室实验来模拟胶体水分散体中的脊扩散，当与盐水溶液接触时，其流变性从纯粘性演变为弹性和脆性。我们发现，直到达到最小曲折度为止，山脊的形状随着扩散率的增加而变得越来越线性。此行为是由轴向故障参数预测Π _˚F，是描述轴向岩石圈脆性和塑性破坏平衡的无量纲数字。低速扩张，故障为主的和快速传播，在地球上和在实验室中的流体侵入主导脊由相同的临界分离Π _˚F值，这表明轴向故障模式共治脊的几何形状。的值Π _˚F也可以计算针对不同的地幔的温度和施加到其他行星或早期地球。对于古生代期间较高的地幔温度，我们的结果排除了在高扩散速度下预测的大型构造板块的形成。