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

岩石圈地幔的变形行为对构造板块的强度具有重要影响。而实验岩石变形研究形成的基础上，我们的理解地幔变形和流变学，基于现场的研究暴露的地幔部分需要调查的流变学和变形的自然变形地幔在更大的空间尺度（10厘米）。最近的野外研究表明了复杂的变形模式，挑战了地幔变形的经典均质流变模型。一个多尺度（厘米到公里），在岩石圈地幔的本地化和变形叠印的过程，导致集成的方法，允许在更大的空间尺度地幔流变学的评估。盾山蛇绿岩带包含多个完整的岩石圈地幔块体，包括红山、红山和盾山，揭示了岩石圈地幔变形的时空模式，阐明了地幔变形、局部化和流变学的基本过程。（1）地幔不均匀性的规模和程度如何？2)是什么作用导致了不同尺度的地幔不均匀性？3)不均匀组构是由时间和/或空间局部变形引起的吗？（4）不均匀变形对组构和结构的保存和大小有何影响？ 这些问题的答案与原始数据的规模和程度的地幔变形的不均匀性，包括结构分析（组构分析、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）、微观结构和质地分析（具有非均质组构的岩石中的组构和组构之间的关系），以及通过分析两种内在的（例如，组成、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。地幔的最上面（岩石圈）部分被认为是形成地球的构造板块中最坚固的部分？s表面。 因此，岩石圈地幔的变形行为对正在进行的和古老的造山过程施加了一级控制。 岩石圈地幔的一部分在造山运动中被抬升和挖出，现在可以在地球上找到？s表面。 这些地方提供了机会，研究地幔过程中发生的变形在自然界的规模。 在这项研究中的主要问题是在何种程度上的变化，在地幔中的不同矿物的确切比例和方向控制的变形行为。 这项工作只能在世界上少数几个有充分接触的地方进行;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，建立上地幔变形的现实和预测模型至关重要。该项目是德克萨斯A M大学和威斯康星州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，它还促进对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一名教员的国际合作。

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.