Collaborative Research: Microstructural and Modeling Constraints on Strain Localization, LPO Development and Rheology of the Upper Mantle

合作研究：应变定位、LPO 发展和上地幔流变学的微观结构和建模约束

• 批准号: 0739010
• 负责人: Peter Kelemen
• 金额: $ 24.13万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-03-01 至 2013-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0739010&HistoricalAwards=false
• 关键词: Collaborative; Research; Microstructural; Modeling; Constraints

A combined microstructural and modeling investigation of mantle shear zones using outcrop scale relationships, tests and explores (a) extrapolation of experimental flow laws, development of lattice preferred orientation, and grain size evolution; and (b) models that predict strain localization and viscous shear heating instabilities. Research focuses on well-exposed shear zones in the Josephine peridotite (Klamath Mountains, Oregon) where shear zone boundaries can be easily identified and finite strain can be quantified by measuring the deflection of pre-existing pyroxene-rich bands. Field and laboratory studies assess models for lattice preferred orientation development and calibrate indicators of shear sense, viscous flow trajectory, and finite strain preserved in peridotite microstructures. Numerical modeling will reproduce strain distribution around shear zones in the Josephine peridotite, using viscoelastic rheology. Olivine flow laws and parameterizations of grain size evolution as a function of stress, strain, strain rate, and grain growth will be incorporated. Rheological properties constrained by observation of the shear zones are compared to the results of the numerical models that incorporate the same rheology. Forward models that approximately reproduce basic field observations will be used to: (a) investigate processes responsible for strain localization and, by analogy, tectonic plate boundaries; and (b) evaluate the hypothesis that viscous shear heating instabilities cause intermediate depth earthquakes in subduction zones, and perhaps other earthquakes in the shallow mantle, such as along oceanic fracture zones.Results from laboratory deformation experiments of peridotite and its constituent minerals are widely used in geodynamical models of the upper mantle. Laboratory studies, however, use samples that are very small in comparison to upper mantle dimensions and are conducted at strain rates much higher than expected in the upper mantle. This study bridges the gap in size and time between laboratory studies and mantle-scale processes, which is essential for understanding upper mantle rheology. This not only further constrains geodynamical modeling, but will also improve understanding of processes controlling intermediate depth earthquakes, post-seismic deformation, preservation of cratonic roots, and the evolution of plate boundaries.

地幔剪切带的显微结构和模拟研究相结合，使用露头比例关系，测试和探索（a）实验流动定律的外推，晶格优选取向的发展，和粒度演化;和（B）模型，预测应变局部化和粘性剪切加热不稳定性。研究的重点是约瑟芬橄榄岩（俄勒冈州的克拉马斯山脉）中暴露良好的剪切带，剪切带边界可以很容易地识别，有限应变可以通过测量预先存在的富含辉石的带的偏转来量化。现场和实验室研究评估模型的晶格择优取向的发展和校准指标的剪切感，粘性流轨迹，并保留在橄榄岩微结构的有限应变。数值模拟将再现应变分布在约瑟芬橄榄岩剪切带，使用粘弹性流变学。橄榄石流动法和参数化的晶粒尺寸演变的应力，应变，应变速率和晶粒生长的函数将被纳入。剪切区的观察约束的流变性能进行比较，将相同的流变学的数值模型的结果。近似再现基本现场观测的正演模型将用于：（a）调查造成应变局部化的过程，并以此类推，调查构造板块边界;以及（B）评估粘性剪切加热不稳定性在俯冲带中引起中等深度地震以及可能在浅地幔中引起其它地震的假设，橄榄岩及其组成矿物的实验室变形实验结果在上地幔动力学模型中得到广泛应用。然而，实验室研究使用的样品与上地幔尺寸相比非常小，并且在比上地幔预期的高得多的应变率下进行。这项研究弥补了实验室研究和地幔尺度过程之间在尺度和时间上的差距，这对于理解上地幔流变学是必不可少的。这不仅进一步限制了地球动力学建模，而且还将提高对控制中等深度地震、震后变形、地震根的保存和板块边界演化的过程的理解。