Unité Matériaux et Transformations, UMR CNRS 8207, Université Lille 1, Villeneuve d'Ascq, France.
Laboratoire d'Etude des Microstructures, CNRS-ONERA, Chatillon, France.
Sci Adv. 2017 Mar 10;3(3):e1601958. doi: 10.1126/sciadv.1601958. eCollection 2017 Mar.
At high pressure prevailing in the lower mantle, lattice friction opposed to dislocation glide becomes very high, as reported in recent experimental and theoretical studies. We examine the consequences of this high resistance to plastic shear exhibited by ringwoodite and bridgmanite on creep mechanisms under mantle conditions. To evaluate the consequences of this effect, we model dislocation creep by dislocation dynamics. The calculation yields to an original dominant creep behavior for lower mantle silicates where strain is produced by dislocation climb, which is very different from what can be activated under high stresses under laboratory conditions. This mechanism, named pure climb creep, is grain-size-insensitive and produces no crystal preferred orientation. In comparison to the previous considered diffusion creep mechanism, it is also a more efficient strain-producing mechanism for grain sizes larger than ca. 0.1 mm. The specificities of pure climb creep well match the seismic anisotropy observed of Earth's lower mantle.
在下地幔中普遍存在的高压条件下，晶格摩擦对位错滑移的阻碍作用变得非常高，正如最近的实验和理论研究所报道的那样。我们研究了尖晶石和布里奇曼石在这种对塑性剪切的高阻力下对下地幔条件下的蠕变机制的影响。为了评估这种影响的后果，我们通过位错动力学模拟位错蠕变。计算结果表明，对于下地幔硅酸盐，位错攀移产生应变是一种主要的蠕变行为，这与实验室条件下高应力下可激活的蠕变行为非常不同。这种机制被称为纯攀移蠕变，它对晶粒尺寸不敏感，不会产生晶体择优取向。与之前考虑的扩散蠕变机制相比，对于大于约 0.1 毫米的晶粒尺寸，它也是一种更有效的应变产生机制。纯攀移蠕变的特殊性很好地匹配了下地幔地震各向异性的观测结果。
