An Experimental Study on the Strength of the Lithosphere: Large-strain shear deformation experiments of olivine + orthopyroxene aggregates

虽然板块构造在地球上有很好的文献记载，但为什么板块构造在地球上有效，而在其他类地行星如金星，火星上无效的原因还没有很好的理解。事实上，板块构造在类地行星上并不是一种明显的构造模式。在类地行星上，由于温度低，近地表层很强，最“自然”的构造模式是所谓的“停滞盖”对流，其中表层是刚性的，不会变形（这是火星和大多数其他行星的情况）。事实上，如果使用岩石圈强度的标准模型，地球上的海洋岩石圈将过于强大，板块构造无法运作。因此，一些弱化过程需要被调用，以了解为什么板块构造在地球上运作。在回顾了地球物质强度的各种新观测结果后，我们认为岩石圈深部的强度减弱是板块构造活动的关键，并将注意力集中在这一问题上，基于我们以前的研究，我们假设第二相矿物斜方辉石（主要矿物为橄榄石）的存在可能对强度减弱有关键影响。因此，我们将进行系统的实验研究的变形的橄榄石和斜方辉石的混合物的各种比例与水含量的范围。流变行为（即，应力-应变关系）和微观结构演变。结果将被解释为一个模型的削弱，并适用于地球和其他类地行星。这项研究的结果将揭示板块构造在地球上运作而不是在其他类地行星上运作的原因。

Although plate tectonics is well documented on Earth, the reason why plate tectonics works on Earth but not on other terrestrial planets such as Venus, Mars is not well understood. In fact, plate tectonics is not an obvious mode of tectonics on Earth-like planets. On Earth-like planets, the near-surface layer is strong because of low temperature and the most 'natural' mode of tectonics is the so-called 'stagnant-lid' convection where the surface layer is rigid and does not deform (this is a case for Mars and most of other planets). In fact, if one uses a standard model of the strength of the lithosphere, the oceanic lithosphere on Earth will be too strong for plate tectonics to operate. Consequently, some weakening processes need to be invoked in order to understand why plate tectonics operates on Earth. After reviewing various new observations on the strength of Earth materials, we believe that the reduction in the strength in the deep lithosphere is a key to the operation of plate tectonics, and focus our attention to this issue.Based on our previous studies, we hypothesize that the presence of a secondary phase mineral orthopyroxene (the primary one being olivine) might have a key influence on the weakening. Consequently, we will conduct systematic experimental studies on deformation of a mixture of olivine and orthopyroxene for various ratios with a range of water contents. Rheological behavior (i.e., the stress-strain relationship) and the micro-structural evolution will be investigated. The results will then be interpreted by a model of weakening, and applied to Earth and other terrestrial planets. The results of this study will shed some lights on the reason for the operation of plate tectonics on Earth but not on other terrestrial planets.