The strength of the lithosphere is typically modelled based on constitutive equations for steady-state flow. However, models of lithospheric flexure reveal differences in lithospheric strength that are difficult to reconcile based on such flow laws. Recent rheological data from low-temperature deformation experiments on olivine suggest that this discrepancy may be largely explained by strain hardening. Details of the mechanical data, specifically the effects of temperature-independent back stresses stored in the samples, indicate that strain hardening in olivine occurs primarily due to long-range elastic interactions between dislocations. These interpretations provided the basis for a new flow law that incorporates hardening by development of back stress. Here, we test this hypothesis by examining the microstructures of olivine samples deformed plastically at room temperature either in a deformation-DIA apparatus at differential stresses of 10.2 GPa. High-angular resolution electron backscatter diffraction maps reveal the presence of geometrically necessary dislocations with densities commonly above 10$^{14}$ m$^{-2}$ and intragranular heterogeneities in residual stress on the order of 1 GPa in both sets of samples. Scanning transmission electron micrographs reveal straight dislocations aligned along slip bands and interacting with dislocations of other types that act as obstacles. The stress heterogeneities and accumulations of dislocations along their slip planes are consistent with strain hardening resulting from long-range back-stresses acting between dislocations. These results corroborate the mechanical data in supporting the form of the new flow law for low-temperature plasticity and provide new microstructural criteria for identifying the operation of this deformation mechanism in natural samples.

中文翻译：

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橄榄石低温塑性过程中的位错相互作用及其对岩石圈强度演化的影响

岩石圈的强度通常基于稳态流动的本构方程进行建模。然而，岩石圈弯曲模型揭示了岩石圈强度的差异，这些差异难以根据这种流动规律进行协调。最近橄榄石低温变形实验的流变数据表明，这种差异可能在很大程度上是由应变硬化来解释的。机械数据的详细信息，特别是存储在样品中的与温度无关的背应力的影响，表明橄榄石中的应变硬化主要是由于位错之间的长程弹性相互作用。这些解释为新的流动定律提供了基础，该流动定律结合了背应力发展引起的硬化。这里，我们通过检查在室温下塑性变形的橄榄石样品的微观结构来测试这一假设，或者在 10.2 GPa 不同应力下的变形 DIA 设备中。高角分辨率电子背散射衍射图揭示了几何上必要的位错的存在，密度通常高于 10$^{14}$m$^{-2}$ 和残余应力的颗粒内不均匀性在两组中都为 1GPa样品。扫描透射电子显微照片揭示了沿着滑移带排列的直位错，并与作为障碍物的其他类型的位错相互作用。应力异质性和位错沿其滑移面的积累与位错之间作用的长程背应力引起的应变硬化一致。