The Influence of Water on the Strength of Olivine Dislocation Slip Systems
The Influence of Water on the Strength of Olivine Dislocation Slip Systems
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DOI：
10.1029/2019jb017436
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发表时间：
2019-07-01
影响因子：
3.9
通讯作者：
Wheeler, John
中科院分区：
文献类型：
--
作者：
Tielke, Jacob;Mecklenburgh, Julian;Wheeler, John
富含橄榄石的岩石中晶格择优取向（LPO）的性质强烈影响地球上地幔的许多重要物理性质。在不同水逸度条件下对富含橄榄石的岩石进行变形实验时，观察到不同类型的 LPO 的形成。不同LPO类型的发展归因于橄榄石中的位错滑移系统对水逸度具有不同的敏感性，但这一假设尚未得到直接检验。为了测量水逸度对橄榄石位错滑移系相对强度的影响，我们在无水或含水条件下对橄榄石单晶进行了一系列变形实验。晶体被定向为使用直接剪切几何激活（010）[100]、（001）[100]或（100）[001]位错滑移系统，这允许隔离单滑移系统，这与压缩实验中激活的多个系统形成鲜明对比。变形后电子背散射衍射分析揭示了与通过激活滑移系统上位错运动发生的变形一致的取向梯度。所有研究方向的晶体都表现出水解弱化，但激活 (001)[100] 滑移系统取向的晶体表现出最大程度的弱化。这些结果与水引起的富含橄榄石岩石因位错蠕变而引起的 LPO 变化一致。从实验中获得的流变数据可用于改进地幔中LPO演化模型，这对于地球内部结构成像和预测地球构造板块的运动至关重要。
The nature of lattice-preferred orientation (LPO) in olivine-rich rocks strongly influences many important physical properties of Earth's upper mantle. Different LPO types have been observed to develop in deformation experiments on olivine-rich rocks carried out at different water fugacity conditions. The development of the different LPO types has been attributed to dislocation slip systems in olivine having different sensitivities to water fugacity, but this hypothesis has not been directly tested. To measure the influence of water fugacity on the relative strengths of olivine dislocation slip systems, we carried out a series of deformation experiments on olivine single crystals under either anhydrous or hydrous conditions. The crystals were oriented to activate either the (010)[100], (001)[100], or (100)[001] dislocation slip systems using a direct shear geometry, which allows for isolation of single slip systems, in contrast to the multiple systems activated in experiments carried out in compression. Post-deformation electron backscatter diffraction analyses reveal orientation gradients consistent with deformation occurring via the motion of dislocations on the activated slip systems. Crystals in all of the investigated orientations exhibit hydrolytic weakening, but crystals oriented to activate the (001)[100] slip system exhibit the largest degree of weakening. These results are consistent with a water-induced change in LPO in olivine-rich rocks deforming by dislocation creep. The rheological data obtained from the experiments can be used to improve models of LPO evolution in Earth's mantle, which is critical for imaging the structure of Earth's interior and predicting the movement of Earth's tectonic plates.