Continued Investigation of Rheological Behavior of Clinopyroxene and Clinopyroxene-Olivine Aggregates Under Hydrous Conditions: Implications for Crustal and Mantle Dynamics

含水条件下单斜辉石和单斜辉石-橄榄石聚集体流变行为的继续研究：对地壳和地幔动力学的影响

• 批准号: 0439747
• 负责人: David Kohlstedt
• 金额: --
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-02-15 至 2009-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0439747&HistoricalAwards=false
• 关键词: Continued; Investigation; Rheological; Behavior; Clinopyroxene

++This proposal involves an experimental investigation of the high-temperature, high-pressure strength of aggregates of clinopyroxene, an important mineral in both the lower crust and the upper mantle, and of aggregates of clinopyroxene plus olivine. Recent analyses of earthquake depth distributions and gravity anomalies on continents conclude that the lower crust is, in general, stronger than the uppermost mantle. This point of view is contrary to the jelly-sandwich model of the continental lithosphere in which a weak lower crust lies between a strong upper crust and a strong upper mantle such that the strength of the continental lithosphere lies in the mantle rather than in the crust. This research projects explores the proposition that the relative strengths of lower crust and upper mantle depend on the presence or absence of water. Little is known about the strength of clinopyroxene relative to that of olivine, even when the two phases are present in the same rock. Recent experiments suggest that clinopyroxene is stronger than olivine under anhydrous conditions but weaker than olivine in hydrous environments. A careful investigation of the water concentration dependence of the viscosity of clinopyroxene and clinopyroxene + olivine rocks is critical in order to address these issues and to model the geodynamical and geochemical behavior and evolution of the lower crust and upper mantle. The effect of water on the viscosity of rocks composed of clinopyroxene and clinopyroxene + olivine is emphasized, because even a small amount of water dramatically weakens nominally anhydrous minerals. In most studies, the water-weakening effect has been treated as an 'on-off' process - if water is present, rocks are weak; if water is absent, rocks are strong. Recent experiments demonstrate that the viscosity of olivine-rich rocks is a factor of more than 10 smaller in water-rich environments (e.g., the mantle wedge above a subducting slab) than in water-under saturated settings (e.g., mantle beneath a mid-ocean ridge). The proposed research builds on this observation, on published investigations of the deformation behavior of dry clinopyroxene-rich rocks, and on our initial results that reveal a significantly larger water-weakening effect in clinopyroxene than in olivine. To apply laboratory results to processes occurring at depth in the Earth, detailed flow laws are essential in order to describe strain rate (i.e., viscosity) as a function of water concentration as well as differential stress, grain size, temperature, and pressure in both the diffusion and the dislocation creep regimes. Water concentrations are determined by micro-infrared analyses, microstructures produced by deformation are analyzed using optical and electron microscopy, and fabrics are measured using electron backscattered diffraction.

++这项建议涉及对单斜辉石（下地壳和上地幔中的一种重要矿物）聚集体和单斜辉石加橄榄石聚集体的高温高压强度进行实验研究。 最近对大陆地震深度分布和重力异常的分析得出结论，下地壳一般比上地幔更强。 这一观点与大陆岩石圈的“三明治”模型相反，在“三明治”模型中，一个软弱的下地壳位于一个强大的上地壳和一个强大的上地幔之间，因此大陆岩石圈的强度是在地幔而不是在地壳中。 本研究项目探讨了下地壳和上地幔的相对强度取决于水的存在与否的命题。 关于单斜辉石相对于橄榄石的强度知之甚少，即使这两相存在于同一岩石中。 最近的实验表明，单斜辉石在无水条件下比橄榄石强，但在含水环境中比橄榄石弱。 为了解决这些问题，并模拟下地壳和上地幔的地球动力学和地球化学行为和演化的水浓度依赖的单斜辉石和单斜辉石+橄榄石岩石的粘度的仔细调查是至关重要的。 水对由单斜辉石和单斜辉石+橄榄石组成的岩石的粘度的影响被强调，因为即使是少量的水也会显着削弱名义上的无水矿物。 在大多数研究中，水弱化效应被视为一个“开-关”的过程-如果有水，岩石是脆弱的;如果没有水，岩石是强大的。 最近的实验表明，富含橄榄石的岩石的粘度在富含水的环境中小10倍以上（例如，俯冲板片上方的地幔楔）比在水下饱和环境（例如，洋中脊下的地幔）。 拟议的研究建立在这一观察，对干燥的单斜辉石丰富的岩石的变形行为发表的调查，并在我们的初步结果，揭示了一个显着更大的水弱化效果单斜辉石比橄榄石。 为了将实验室结果应用于地球深处发生的过程，详细的流动定律是必不可少的，以便描述应变率（即，粘度）作为水浓度以及扩散和位错蠕变机制中的差应力、晶粒尺寸、温度和压力的函数。 水的浓度是由显微红外分析，变形产生的微观结构进行了分析，使用光学和电子显微镜，和织物测量使用电子背散射衍射。