Integrated field and numerical investigations on multiscale structures in Earth's lithosphere

我们建议开发大陆岩石圈变形的稳健数值模型，并通过面向野外的自然变形带研究来检验这些模型。我们的目标是建立一个研究小尺度结构的严格框架，以便它们可以用来推断大尺度构造和大陆岩石圈的流变性。**地球在太阳系的类地行星中是独一无二的，因为它具有板块构造，导致板块边界和内部地区的岩石圈板块变形。了解这种形变的物理机制，对于了解地球和其他行星的演化，以及对生活在岩石圈上的人类的福祉，减轻自然灾害，并从岩石圈获得能源、矿产和其他资源，都具有极其重要的科学意义。尽管大陆形变与人类关系密切，而且与我们对海洋岩石圈的了解程度不同，但长期(数百万年)和巨大空间尺度(相当于北美这样的大陆大小)的大陆形变仍然知之甚少。这是因为在广泛的观测尺度上，大陆岩石圈在力学上比大洋岩石圈更加不均匀。经过几十年的研究，我们仍然缺乏有效的手段来处理这种不均匀物体在多尺度上的变形。这项研究将在申请人最新进展的基础上，将对变形结构的直接地质调查与基于连续介质细观力学的新的数值模拟方法相结合，该方法解决了非均匀材料的多尺度变形。如何有效地处理流变非均质大陆岩石圈的变形并模拟伴随的多尺度构造的发展，一直是构造地质学和构造学领域最基本的问题，也是其发展的瓶颈。40多年来，结构和构造界一直求助于单比例模型(主要是同质的和运动学的)，尽管它们长期以来一直被认为非常不现实。问题的关键是找到一种严格的方法来解决像大陆岩石圈这样的非均质材料中流场的巨大变异性。最近，申请人成功地为非牛顿粘性材料(被认为是地球岩石圈的最好代表)开发了基于微观力学的多阶幂定律方法(MOPLA)，首次将织物建模建立在严格的力学基础上。这项建议需要资金1)将MOPLA发展成一个更稳健的模型，一个自洽的模型，其中包含了变形过程中由于织物堆积而产生的流变学演变的显著影响，以及2)通过在明确定义的自然变形区进行实地研究来检验模型预测。这项研究的成果有望成为构造地质学和构造学的一项里程碑式的成就。研究目标与我的长期研究目标一致，即建立一种研究微小结构的理论、数值和现场综合方法。研究活动将包括数值模式的理论制定和实施以及实地和实验室工作。这些活动将涉及许多研究生和其他研究助理。因此，这项研究为本科生、研究生和初级科学家提供了一个讲授高级野外工作、实验室和计算技能的平台，将科学调查与新科学家的培训结合起来。

We propose to develop robust numerical models for the deformation of the continental lithosphere and to test these models by field-oriented studies of natural deformation zones. Our goal is to establish a rigorous framework for studying small-scale structures so that they can be used to infer large-scale tectonics and the rheology of the continental lithosphere.**The Earth is unique among the terrestrial planets in the solar system in that it has plate tectonics which causes lithospheric plates to deform in plate boundary and interior regions. Understanding the physics of this deformation is of paramount significance both scientifically, for understanding the evolution of Earth and other planets, and practically for the welfare of human beings who live on the lithosphere, mitigate natural hazards, and derive energy, mineral, and other resources from it. Despite its close relationship to humanity and in contrast to our level of understanding of the oceanic lithosphere, continental deformation over long terms (millions of years) and across vast spatial scales (comparable to the size of a continent like the North America) remains poorly understood. This is because the continental lithosphere is far more heterogeneous mechanically than the oceanic lithosphere on a wide range of observation scales. After many decades of research, we still lack an effective means to tackle the deformation of such a heterogeneous body on multiscales. This research will build on the applicant's recent progress and combine direct geological investigations on deformation structures, which are "signatures" of past lithospheric deformation, with a novel numerical modeling approach based on continuum micromechanics, which addresses the multiscale deformation of heterogeneous materials. **How to tackle effectively the deformation of a rheologically heterogeneous continental lithosphere and to model the accompanying development of multiscale structures have been most fundamental issues in the field of structural geology and tectonics, and bottle necks to its advances. For over 4 decades, the structural and tectonics community has resorted to single-scale models (mostly homogeneous and of a kinematic nature), although they have long been recognized as highly unrealistic. The key to the problem is to find a rigorous means to address the great variability in the flow field in a heterogeneous material like the continental lithosphere. Recently, the applicant has succeeded in developing a MultiOrder Power Law Approach (MOPLA) based on micromechanics for non-Newtonian viscous materials (believed to be the best representation of Earth's lithosphere) which, for the first time, places fabric modeling on rigorous mechanical grounds. This proposal requests funds 1) to develop MOPLA into a more robust model, a self-consistent one that incorporates the significant effect of the evolving rheology due to fabric buildup in the process of deformation, and 2) to test the model predictions by field studies in well-defined natural deformation zones. The outcome of this research is expected to be a landmark achievement in structural geology and tectonics. The research objectives align with my long-term research goal to establish an integrated theoretical, numerical, and field methodology for studying small structures. The research activities will include theoretical formulation and implementation of numerical models and field and laboratory work. These activities will involve many graduate students and other research associates. Thus the research provides a platform for teaching advanced fieldwork, laboratory, and computational skills to undergraduate, graduate students, and junior scientists, combining scientific investigation with the training of new scientists.