Collaborative Research: Effects of Structural and Compositional Heterogeneity on Upper Mantle Deformation and Rheology

合作研究：结构和成分异质性对上地幔变形和流变学的影响

• 批准号: 1050044
• 负责人: Julie Newman
• 金额: $ 23.74万
• 依托单位: Texas A&M Research Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-03-01 至 2015-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1050044&HistoricalAwards=false
• 关键词: Collaborative; Research; Effects; Structural; Compositional

The deformational behavior of the lithospheric mantle exerts a critical effect on the strength of the tectonic plates. Whereas experimental rock deformation studies form the basis of our understanding of mantle deformation and rheology, field-based studies of exposed mantle sections are needed to investigate the rheology and deformation of naturally deformed mantle at larger spatial scales ( 10 cm). Recent field studies have illustrated complex patterns of deformation that challenge a classical homogeneous rheological model for mantle deformation. A multi-scale (cm to km), integrated approach of the processes that result in localization and deformational overprinting in lithospheric mantle, allows an assessment of mantle rheology at larger spatial scales. The Dun Mountain ophiolite belt contains multiple intact blocks of lithospheric mantle - including the Red Hills, Red Mountain, and Dun Mountain - that reveal spatial and temporal patterns of deformation in naturally deformed lithospheric mantle and elucidate fundamental processes of mantle deformation, localization, and rheology.First-order tectonic questions about deformation in the lithospheric mantle addressed by this research include: 1) What is the scale and extent of mantle heterogeneity?; 2) What processes result in mantle heterogeneity at different scales?; 3) Do heterogeneous fabrics result from temporally and/or spatially localized deformation?; and 4) What is the effect of heterogeneous deformation on fabric and texture preservation and magnitude? These questions are answered with primary data on the scale and extent of mantle deformational heterogeneity including structural analyses (fabric analysis, compositional and structural domain characterization, identification of localizing or overprinting phenomena, strain analysis, estimates of effective viscosity), microstructural and textural analyses (relationship between texture and fabric in rocks with heterogeneous fabrics), and analyses of deformation processes by analyzing both intrinsic (e.g., composition, melt fraction, grain size) and extrinsic (e.g., pressure, temperature, stress, oxygen fugacity) rock characteristics.The uppermost (lithospheric) part of the mantle is thought to be the strongest part of the tectonic plates that form the Earth?s surface. As such, the deformational behavior of the lithospheric mantle exerts a first-order control on ongoing and ancient mountain building processes. Portions of the lithospheric mantle are uplifted and exhumed during mountain building events and can now be found on the Earth?s surface. These localities offer the opportunity to study mantle processes at the scales at which deformation occurs in nature. The major question in this research is the extent to which variations in the exact proportion and orientation of different minerals in the mantle control the deformational behavior. This work can only be done in a few places in the world with sufficient exposure; the proposed work will take place in New Zealand. These data are critical in synthesizing results from rock deformation experiments and geophysical observations, to create realistic and predictive models of uppermost mantle deformation.This project is a multidisciplinary collaborative effort between researchers at Texas A&M University and the University of Wisconsin. In addition to the research goals of the project, it is fostering scientific training of graduate and undergraduate students. The project also involves an international collaboration with a faculty member from the University of Otago, New Zealand.

岩石圈地幔的变形行为对构造板块的强度产生关键影响。虽然实验岩石变形研究构成了我们理解地幔变形和流变学的基础，但需要对暴露的地幔部分进行现场研究，以研究更大空间尺度（10厘米）自然变形地幔的流变和变形。最近的实地研究表明了复杂的变形模式，这对地幔变形的经典均质流变模型提出了挑战。导致岩石圈地幔局部化和变形叠印的过程的多尺度（厘米到公里）综合方法可以在更大的空间尺度上评估地幔流变学。敦山蛇绿岩带包含多个完整的岩石圈地幔块体 - 包括红山、红山和敦山 - 揭示了自然变形的岩石圈地幔变形的时空模式，并阐明了地幔变形、定位和流变的基本过程本研究解决的有关岩石圈地幔变形的一级构造问题包括：1）地幔异质性的规模和程度是多少？ 2）什么过程导致了不同尺度的地幔异质性？ 3）异质织物是否是由时间和/或空间局部变形引起的？ 4) 异质变形对织物和纹理的保留和大小有什么影响？ 这些问题可以通过关于地幔变形异质性的规模和程度的原始数据来回答，包括结构分析（织物分析、成分和结构域表征、局部化或叠印现象的识别、应变分析、有效粘度的估计）、微观结构和结构分析（具有异质结构的岩石中的结构和结构之间的关系），并通过分析内在（例如成分、熔体分数、晶粒尺寸）和外在（例如压力、温度、应力、氧逸度）岩石特征。地幔的最上层（岩石圈）部分被认为是形成地球表面的构造板块中最坚固的部分。 因此，岩石圈地幔的变形行为对正在进行的和古代的造山过程发挥着一级控制作用。 部分岩石圈地幔在造山活动期间被抬升和挖出，现在可以在地球表面找到。 这些地点提供了在自然界发生变形的尺度上研究地幔过程的机会。 这项研究的主要问题是地幔中不同矿物的确切比例和方向的变化在多大程度上控制着变形行为。 这项工作只能在世界上少数几个有足够曝光度的地方进行；拟议的工作将在新西兰进行。 这些数据对于综合岩石变形实验和地球物理观测的结果至关重要，以创建上地幔变形的现实和预测模型。该项目是德克萨斯农工大学和威斯康星大学研究人员之间的多学科合作成果。除了该项目的研究目标外，它还促进研究生和本科生的科学培训。该项目还涉及与新西兰奥塔哥大学的一名教员的国际合作。