Partial Melting at Mantle Conditions: Effect on Elastic, Anelastic, and Plastic Behavior

正如火山和火山岩所证明的那样，地球内部的温度足以融化岩石。在这里，我们想讨论的问题是，部分熔融在确定地幔内区域的机械性质方面有多重要。自板块构造理论早期以来，低剪切波速和低粘度与部分熔融的联系一直是传说的一部分。坚硬的岩石圈定义了由塑性较弱的岩石圈从下向下润滑的板块。地震验证来自无处不在的低速带(至少在大洋板块之下)。该模型隐含的结论是：1)速度和粘度均受少量部分熔融的影响，2)剪切模数比体积模数受影响更大，3)低速区的顶部标志着熔融的开始，而低速区的底部则由部分熔融的消失、粘度和速度的增加来定义。然而，实验室研究并没有完全支持这种对部分熔化的物质反应的观点。虽然部分熔融通常与低地震横波速度带(LVZ)有关，但实验室研究表明，部分熔融可能并不能有效地造成上地幔大的速度变化。我们对这个问题的主要潜在贡献来自于我们在0-15 Gpa和700-2000K的压力范围内评估这些问题的能力，这些问题与低速区的条件有关。以前的研究已经能够承受高达0.3 Gpa的压力。上地幔的低速带在3-7 GPa时出现，上地幔本身延伸到约14 GPa时。因此，我们的研究将是第一个在发现地球现象的条件下分析这些性质的研究。我们将使用国家同步加速器光源的设施，在那里我们已经开发出能够实现这些目标的高压设备。使用X射线探测样品提供了一个压力计来测量应力，并提供了图像来测量应变。我们的系统可以在直流模式下工作，在0.10-0.001赫兹的频率下产生稳定的气流和交流。这项研究将为学生提供学习经验，包括准备博士学位的研究生和专注于暑期研究项目的本科生。这些结果将被用于整个地球科学，作为关于地球内部行为的基本信息。开发的工具将提供给其他研究人员，用于研究材料的强度相关特性。这些工具(软件和硬件)将立即成为COMPRES运行的同步加速器设施的一部分，并可供社区中所有希望使用它们的人使用。这里开发的工具将有助于研究极端环境下的材料特性，并将有助于开发更好的工业材料。

The temperature within the Earth is high enough to melt rocks as evidenced by volcanoes and volcanic rocks. Here we wish to address the question of how important partial melting is in defining the mechanical properties of regions within the mantle. The association of low shear wave velocity and low viscosity with partial melting has been part of the lore since the early days of plate tectonic theory. The strong rigid lithosphere defined the plates that were lubricated from below by the plastically weak aesthenosphere. The seismic verification came from the ubiquitous low velocity zone (at least under oceanic plates). The implicit assertions of this model are 1) velocity and viscosity are both affected by small amounts of partial melting, 2) shear modulus is more affected than bulk modulus, and 3) the top of the low velocity zone marks the onset of melting and the bottom of the low velocity zone is thus defined by the disappearance of partial melting and the increase of both viscosity and velocity. Laboratory studies, however, have not fully endorsed this view of the material response to partial melting. While partial melting is often associated with low seismic shear wave velocity zone (LVZ); laboratory studies have suggested that partial melting may not be effective in creating the large velocity variation in the upper mantle. Our main potential contribution to this problem comes from our capability to assess these questions over the pressure range of 0 - 15 GPa and 700 - 2000K that are relevant to the conditions of the low velocity zone. Previous studies have been capable of pressures of up to 0.3 GPa. The low velocity zone in the upper mantle is found at 3 - 7 GPa and the upper mantle itself extends to about 14 GPa. Thus, our study will be the first that can analyze these properties at the conditions where the Earth phenomena are found. We will use the facilities at the National Synchrotron Light Source where we have developed high-pressure equipment capable of achieving these goals. The use of X-rays to probe the sample provides a piezometer to measure stress and images to measure strain. Our system can operate in a DC mode to generate steady state flow and AC at frequencies of 0.1 - 0.001 Hz. This research will provide a learning experience for students including graduate students in the preparation of their PhD and undergraduates students in the focus of a summer research project. The results will be used throughout the Earth sciences as fundamental information on the behavior of the Earth's interior. The tools that are developed will be made available to other researchers for studying strength related properties of materials. These tools (software and hardware) will immediately become part of the COMPRES operated synchrotron facility and available to all in the community that wish to use them. The tools developed here will be useful for studying material properties under extreme environments and will be useful to develop better industrial materials.