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

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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.