Dislocation Creep of Olivine: Backstress Evolution Controls Transient Creep at High Temperatures
Dislocation Creep of Olivine: Backstress Evolution Controls Transient Creep at High Temperatures
复制标题
橄榄石的位错蠕变：背应力演化控制高温下的瞬时蠕变
DOI：
10.1029/2020jb021325
复制
发表时间：
2021-05-01
影响因子：
3.9
通讯作者：
Kempton, Imogen
中科院分区：
文献类型：
--
作者：
Hansen, Lars N.;Wallis, David;Kempton, Imogen
在高温下对岩石施加应力变化的地球动力学过程中，会发生瞬时蠕变。这种瞬变表现为岩石粘度的演化，直到达到稳定流动。虽然已经提出了几种岩石瞬时蠕变的唯象模型，但控制这种行为的主要微物理过程仍然缺乏约束。为了确定导致橄榄石瞬时蠕变的晶内过程，我们对橄榄石单晶在1,250摄氏度-1,300摄氏度的温度下进行了应力降低测试，在这些实验中，样品在应力降低后经历了随时间变化的反向应变。反向应变的大小与10(-3)相近，并且随着应力降低幅度的增大而增大。变形材料的高角分辨电子背散射衍射分析揭示了与主要滑移系相关的晶格曲率和非均匀应力。力学和显微组织数据与由于位错间背应力的积累和释放而产生的单晶的瞬时蠕变相一致。这些结果使得高温下蠕变的位错-滑移成分得以分离，我们利用这些数据校准了橄榄石的流动定律，以描述在较宽的温度范围内蠕变的滑移成分。我们认为，这一流动定律可以用来估计橄榄石的瞬时蠕变和稳态粘度，其瞬时演化受背应力的演化控制。该模型能够预测瞬变(正反向)的变化性和以前工作中观察到的载荷松弛响应。简单语言摘要在高温和长时间尺度下，岩石可以以类似于粘性流体的方式流动。如果驱动岩石流动的地球上的应力突然发生变化(如地震后)，岩石的粘度就会发生变化和演化。粘度的这种变化会影响应力松弛或重新开始积累的速度。我们目前还不了解控制这种粘度演变的潜在物理因素，这降低了我们预测和评估地球内部流动的许多方面的能力。
Transient creep occurs during geodynamic processes that impose stress changes on rocks at high temperatures. The transient is manifested as evolution in the viscosity of the rocks until steady-state flow is achieved. Although several phenomenological models of transient creep in rocks have been proposed, the dominant microphysical processes that control such behavior remain poorly constrained. To identify the intragranular processes that contribute to transient creep of olivine, we performed stress-reduction tests on single crystals of olivine at temperatures of 1,250 degrees C-1,300 degrees C. In these experiments, samples undergo time-dependent reverse strain after the stress reduction. The magnitude of reverse strain is similar to 10(-3) and increases with increasing magnitude of the stress reduction. High-angular resolution electron backscatter diffraction analyses of deformed material reveal lattice curvature and heterogeneous stresses associated with the dominant slip system. The mechanical and microstructural data are consistent with transient creep of the single crystals arising from accumulation and release of backstresses among dislocations. These results allow the dislocation-glide component of creep at high temperatures to be isolated, and we use these data to calibrate a flow law for olivine to describe the glide component of creep over a wide temperature range. We argue that this flow law can be used to estimate both transient creep and steady-state viscosities of olivine, with the transient evolution controlled by the evolution of the backstress. This model is able to predict variability in the style of transient (normal vs. inverse) and the load-relaxation response observed in previous work.Plain Language Summary At high temperatures and over long timescales, rocks can flow in a similar manner to viscous fluids. If the stresses in Earth that drive the flow of rocks change suddenly in magnitude (e.g., after an earthquake), the viscosity of the rock changes and evolves. This evolution in viscosity influences how quickly the stress is relaxed or starts to build up again. We do not currently understand the underlying physics controlling this evolution in viscosity, which reduces our ability to predict and evaluate many aspects of flow in Earth's interior.