Melt segregation in a deforming partially molten rock - an experimental investigation of the consequences of viscous anisotropy

变形部分熔融岩石中的熔体偏析——粘性各向异性后果的实验研究

• 批准号: 1520647
• 负责人: David Kohlstedt
• 金额: $ 23.48万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1520647&HistoricalAwards=false
• 关键词: Melt; segregation; deforming; partially; molten

Melt segregation in a deforming partially molten rock ? An experimental investigation of the consequences of viscous anisotropy Kohlstedt - Extraction of melt from mantle rocks composed of solid grains plus 1 or 2% melt results in eruption of magma at Earth?s surface. This process controls the chemical and physical evolution of our planet. Since processes occurring at great depths are not directly observable, much of our understanding of the dynamics of partially molten regions of Earth?s interior relies on numerical/computer models of the behavior of partially molten rocks. The starting point for models of a mechanically weak melt in a strong but deformable rock is known as two-phase flow theory. Application of this theory to large-scale processes occurring far below Earth?s surface requires equations describing the viscosity (strength) and the rate at which melt flows through a rock. An important test of the validity of models used to describe the interactions of deformation, melt distribution, and melt migration in the mantle is their ability to explain phenomena observed in laboratory experiments on partially molten rocks.A fundamental breakthrough in the theory describing the dynamics of partially molten rocks occurred with the publication of three fundamental papers in 2009. These papers explored the implications of anisotropic viscosity (i.e., the directional dependence of the strength of a rock) on melt distribution during deformation. It was hypothesized that viscosity (strength) should be anisotropic because pockets of melt become aligned during deformation. Based on this anisotropic grain-scale melt distribution, it was predicted that melt-rich bands should develop in deforming rocks, consistent with previously experimental observations. This analysis also predicted that solid and melt should segregate from regions of low stress to regions of high stress. Our recent experiments, in fact, demonstrated this behavior in partially molten samples deformed in torsion in our laboratory. A key aspect of our research is a synergistic collaboration with scientists at the University of Oxford (computer models) and Tokyo (theory). Through our cooperative efforts, models based on two-phase flow theory will be tested against experimental observations in order to advance our understanding of how melt flows in Earth?s mantle. While agreement between theory and experiment is clearly important, discrepancies represent an avenue for progress in refining theory. Discrepancies between theoretical prediction and experimental observation represent an opportunity to refine our understanding of the grain-scale mechanics of partially molten rocks. Thus, well-designed experiments with detailed analysis of melt distribution, melt segregation, and mechanical properties are essential. A unique aspect of this research is our involvement in STEM outreach in Mexico though ?Clubes de ciencia México?, an organization of science outreach and mentoring for high school and undergraduate students in Mexico. The science clubs are one-week long, very interactive workshops designed to initiate students to science and research; special focus is given to scientific reasoning and ethics. A recent workshop on ?How do rocks flow?? illustrated the necessity of experimental studies for understanding our planet?s evolution. Outreach will continue through a website and outreach workshops, using our current experimental investigations to explain the implications of experimental research for understanding large-scale dynamics of our planet.

在变形的部分熔融的岩石中的熔体偏析？粘滞各向异性后果的实验研究科尔施泰特-从地幔岩石中提取熔体的固体颗粒加上1或2%的熔体的结果在地球岩浆喷发？s表面。这个过程控制着我们星球的化学和物理演化。由于在很深的地方发生的过程不能直接观察到，我们对地球部分熔融区域的动力学的理解大部分是？的内部依赖于部分熔融岩石行为的数值/计算机模型。在坚固但可变形的岩石中的机械弱熔体模型的出发点被称为两相流理论。将这一理论应用于发生在地球深处的大规模过程？表面需要描述粘度（强度）和熔体流过岩石的速率的方程。地幔中变形、熔体分布和熔体迁移相互作用模型的有效性的一个重要检验是其解释实验室部分熔融岩石实验中观察到的现象的能力。2009年发表的三篇基础论文在描述部分熔融岩石动力学的理论上取得了根本性突破。这些论文探讨了各向异性粘度的含义（即，岩石强度的方向依赖性）在变形过程中对熔体分布的依赖性。假设粘度（强度）应该是各向异性的，因为熔体袋在变形期间变得对齐。基于这种各向异性的颗粒尺度的熔体分布，它被预测，熔体丰富的带应发展变形岩石，与以前的实验观察一致。该分析还预测，固体和熔体应该从低应力区域分离到高应力区域。事实上，我们最近的实验在我们实验室的扭转变形的部分熔融样品中证明了这种行为。我们研究的一个关键方面是与牛津大学（计算机模型）和东京大学（理论）的科学家进行协同合作。通过我们的合作努力，基于两相流理论的模型将根据实验观察进行测试，以促进我们对地球上熔体流动的理解。的斗篷。虽然理论和实验之间的一致性显然很重要，但差异代表了改进理论的一条途径。理论预测和实验观察之间的差异代表了一个机会，以完善我们的部分熔融岩石的颗粒尺度力学的理解。因此，精心设计的实验，详细分析熔体分布，熔体偏析和机械性能是必不可少的。这项研究的一个独特方面是我们在墨西哥参与STEM推广，虽然？梅西科城市俱乐部？，一个为墨西哥高中和本科生提供科学推广和指导的组织。科学俱乐部是为期一周的，非常互动的研讨会，旨在启动学生的科学和研究;特别注重科学推理和道德。最近的一次研讨会在？岩石是如何流动的？说明了实验研究对了解我们的星球的必要性？的进化。外联将继续通过一个网站和外联讲习班，利用我们目前的实验研究来解释实验研究对理解我们星球的大规模动态的影响。