Melt Network Geometry in Stressed, Partially Molten Mantle Rocks: Implications for Seismic Anisotropy

受应力、部分熔融地幔岩石中的熔融网络几何形状：对地震各向异性的影响

• 批准号: 1753482
• 负责人: Matej Pec
• 金额: $ 38万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-01 至 2022-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1753482&HistoricalAwards=false
• 关键词: Melt; Network; Geometry; Stressed; Partially

Melting and deformation are intimately coupled in nature and work in concert to accommodate plate tectonic movements. These movements are associated with earthquakes and volcanic eruptions which are one of the primary natural hazards to human settlements. It is therefore important that we understand how melt and deformation interact deep in our planet. Since we are unable to directly observe this interaction, we rely on the interpretation of various remote sensing surveys. One powerful means of interrogating our planet's interior is to study the sound waves propagating through the Earth after an earthquake. The speed at which waves propagate as well as their damping depends on the details of how melt and crystallized minerals are aligned. This information can therefore be used to detect the spatial extent of partially molten domains as well as their flow direction deep in Earth's interior. The investigator's research aims at constraining the basic physical principles that govern melt and mineral alignment in deforming partially molten rocks through a series of laboratory experiments. The research funded by this proposal will form the basis of a doctoral dissertation of a graduate student in the PI's laboratory and will introduce the student to the scientific method and thinking. Additionally, an analogue experiment will be developed to illustrate the influence of partial melting on sound wave propagation. This experiment will be used in undergraduate and graduate classes taught by the PI as well as for outreach to general public during events like the Cambridge Science Festival. Melting occurs in actively deforming regions of the Earth such as subduction zones and mid-oceanic ridges and affects much of the chemical exchange between mantle, crust and atmosphere. The presence of melt strongly influences the mechanical and transport properties of partially molten rocks and can produce a signature detectable by remote sensing. Remote sensing of plate boundaries gives us a wealth of information about the fundamental forces that drive plate tectonics and forms the basis for testing geodynamic hypotheses. The primary goal of this research is to elucidate the (i) influence of deformation on grain-scale melt network topology and (ii) the influence of deformation with melt present on the evolution of crystallographic preferred orientation (CPO) in olivine, the most abundant mineral in the lithospheric mantle. Both stress-driven melt preferred orientation (MPO) as well as CPO evolve on different length- and time-scales and contribute to the integrated seismic signature of deforming partially molten rocks in nature. The team will synthesize fine-grained olivine rocks with approximately 3 vol% of mid ocean ridge basalt added as a melt phase and deform these rocks in general shear under pressure and temperature conditions typical for the upper mantle (T = 900 - 1200 degrees C, P = 0.3 - 2 GPa). Constant load experiments at load levels covering at least one order of magnitude will be performed to study the effect of stress on the grain-scale melt network topology. Several experiments at a constant stress level will be taken to different finite strains to elucidate the influence of strain on MPO and CPO. Conducting such a comprehensive series of well-controlled experiments will constrain the influence of stress and strain on both MPO as well as CPO development in partially molten mantle rocks. The derived quantitative microstructural data will be used to calculate the seismic signature of the rocks based on several theoretical models. Establishing correlations between measured microstructural quantities and external forces in experiments will provide tight constraints for theoretical models of deforming solid-liquid composites and will facilitate extrapolation of laboratory data to natural conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

熔融和变形在本质上是密切相关的，并协同工作以适应板块构造运动。这些运动与地震和火山爆发有关，这是人类住区的主要自然灾害之一。因此，了解地球深处的融化和变形是如何相互作用的，这一点非常重要。由于我们无法直接观察到这种相互作用，我们依赖于各种遥感调查的解释。研究地球内部构造的一个有力手段是研究地震后在地球上传播的声波。波的传播速度及其阻尼取决于熔融矿物和结晶矿物排列的细节。因此，这些信息可以用来探测部分熔融区域的空间范围，以及它们在地球内部深处的流动方向。研究者的研究目的是通过一系列的实验室实验来限制在变形部分熔融岩石中控制熔体和矿物排列的基本物理原理。由该提案资助的研究将成为PI实验室研究生博士论文的基础，并将向学生介绍科学方法和思维。此外，还将进行模拟实验来说明部分熔化对声波传播的影响。这个实验将用于PI教授的本科生和研究生课程，以及在剑桥科学节等活动期间向公众推广。熔融发生在地球的活跃变形区域，如俯冲带和洋中脊，并影响了地幔、地壳和大气之间的大部分化学交换。熔体的存在强烈影响部分熔融岩石的力学和输运性质，并可产生遥感可探测的特征。对板块边界的遥感为我们提供了有关驱动板块构造的基本力量的丰富信息，并为检验地球动力学假设奠定了基础。本研究的主要目的是阐明(i)变形对颗粒尺度熔体网络拓扑结构的影响；（ii）有熔体存在的变形对岩石圈地幔中最丰富的矿物橄榄石的结晶学优先取向（CPO）演化的影响。应力驱动的熔融优先取向（MPO）和CPO在不同的长度和时间尺度上演化，构成了自然界部分熔融岩石变形的综合地震特征。该团队将合成细粒橄榄岩，并在熔融阶段加入约3卷%的中洋脊玄武岩，并在上地幔典型的压力和温度条件下（T = 900 - 1200摄氏度，P = 0.3 - 2 GPa）在一般剪切下使这些岩石变形。在至少一个数量级的载荷水平上进行恒载实验，以研究应力对晶粒尺度熔体网络拓扑结构的影响。在恒定应力水平下对不同的有限应变进行了多次实验，以阐明应变对MPO和CPO的影响。开展如此全面的一系列控制良好的实验，将抑制应力和应变对部分熔融地幔岩石中岩浆岩浆形成和岩浆岩浆形成的影响。所得的定量微观结构数据将用于基于几种理论模型计算岩石的地震特征。在实验中建立测量的微观结构量与外力之间的相关性将为变形固液复合材料的理论模型提供严格的约束，并将有助于将实验室数据外推到自然条件。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Radial Melt Segregation During Extrusion of Partially Molten Rocks

部分熔岩挤压过程中的径向熔体偏析

• DOI: 10.1029/2018gc008168
• 发表时间: 2019
• 期刊: Geosystems
• 作者: Quintanilla‐Terminel, Alejandra;Dillman, Amanda M.;Pec, Matej;Diedrich, Garrett;Kohlstedt, David L.
• 通讯作者: Kohlstedt, David L.