Experimental deformation of mica at high temperature under hydrothermal conditions

水热条件下云母高温变形实验

• 批准号: NE/E002919/1
• 负责人: Ernest Rutter
• 金额: $ 41.81万
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE002919%2F1
• 关键词: Experimental; deformation; mica; temperature; under

Summary Natural geodynamic processes include mountain building, the development of sedimentary basins, and processes at plate margins that can lead either to earthquakes or to slow, steady slippage on faults. In all of these rocks become deformed. Our ability to understand processes of natural rock deformation depends on being able to carry out deformation (fracture and flow) experiments in the laboratory under high pressures and temperatures that simulate natural conditions at depth in the Earth. From such studies over the past 50 years it has become possible to predict variation of rock strength with depth for simple models of lithospheric structure, and this has led to improved understanding of geodynamic processes. In such models the simplifying assumption has usually been made that the strength of the outer part of the Earth's crust is determined by quartz, the lower crust by feldspar and the upper mantle by olivine. The role of minerals of the mica group has received little consideration, despite such minerals being common in mudstones and their equivalent metamorphic rocks and being abundant in many major fault zones. Recent studies in this laboratory and elsewhere suggest that mica minerals may become much weaker than previously suspected at mid-crustal depths (about 15 km) and below. This is due to activation of a previously unsuspected process of viscous sliding parallel to the natural sheet structure of the mineral. If this process can be characterized and verified it will have substantial implications for our understanding of the strength of the continental crust and of all geological processes that depend upon rock deformation. Here we propose a new program of high pressure/temperature experiments aimed at fully characterizing this type of viscous flow. Shearing experiments will be done at temperatures ranging up to the onset of chemical breakdown of mica minerals by dehydroxylation and ultimately melting, using high water pressures to suppress the breakdown to the upper end of the temperature range (400 to 800 degC). This will maximize the temperatures that we can use, for rock deformation processes operate faster at higher temperatures. We can then extrapolate from relatively short duration (up to a few weeks) laboratory experiments at high temperatures to the lower temperature environment but longer timescale of natural rock deformation. We will use both synthetic, polycrystalline mica 'rocks', but also single mica crystals, which should best display the viscous creep process. We will determine how the rate of deformation of the mica specimens depends on applied stress, temperature, confining pressure (depth of burial) and pore water pressure. For experimentally deformed samples we will use scanning and transmission electron microscopy plus microchemical techniques to determine mechanisms of deformation and any chemical changes that accompany it. We will also carry out complementary study of naturally deformed micaceous rocks to help verify the applicability of our experimental results, and carry out extrapolation of our experimental data to geological deformation conditions to deduce the impact of mica deformation for natural geodynamic processes.

自然地球动力学过程包括造山、沉积盆地的发展和板块边缘的过程，这些过程可能导致地震或在断层上缓慢而稳定地滑动。所有这些岩石都变形了。我们理解天然岩石变形过程的能力取决于能够在实验室中进行高压和高温下的变形(破裂和流动)实验，模拟地球深处的自然条件。从过去50年来的这类研究中，可以用简单的岩石圈结构模型来预测岩石强度随深度的变化，这导致了对地球动力学过程更好的理解。在这样的模型中，通常作出简化的假设，即地壳外层的强度由石英决定，下层地壳由长石决定，上地幔由橄榄石决定。云母族矿物的作用很少被考虑，尽管这种矿物在泥岩和相当于变质岩中很常见，并且在许多主要断裂带中都很丰富。该实验室和其他地方最近的研究表明，在地壳中层(约15公里)及以下，云母矿物可能会变得比之前怀疑的要弱得多。这是由于激活了之前未被怀疑的平行于矿物天然片层结构的粘性滑动过程。如果这一过程能够被描述和证实，它将对我们理解大陆地壳的强度和所有依赖于岩石变形的地质过程产生重大影响。在这里，我们提出了一种新的高压/高温实验方案，旨在全面描述这种粘性流动。剪切实验将在云母矿物开始通过脱羟基并最终熔化的化学分解的温度下进行，使用高水压将分解抑制到温度范围的上端(400至800摄氏度)。这将使我们可以使用的温度最大化，因为岩石变形过程在更高的温度下运行得更快。然后我们可以从高温下相对较短的持续时间(最多几周)的实验室实验推断到较低的温度环境，但自然岩石变形的时间尺度较长。我们将使用合成的多晶云母‘岩石’，但也使用单云母晶体，这应该是最好的粘性蠕变过程。我们将确定云母样品的变形率如何取决于施加的应力、温度、围压(埋深)和孔隙水压力。对于实验变形的样品，我们将使用扫描和透射电子显微镜加上微量化学技术来确定变形机制和伴随其而来的任何化学变化。我们还将对自然变形的云母岩进行补充研究，以帮助验证我们的实验结果的适用性，并将我们的实验数据外推到地质变形条件，以推断云母变形对自然地球动力学过程的影响。