Collaborative Research: Geodynamic implications of imaged upper mantle heterogeneity beneath the Western United States

本项目研究美国西部地幔流动的原因和后果。需要考虑几个相互作用的地质活动的时空尺度：(1)与北美板块运动有关的环流，(2)美国东部下地幔中老法拉龙板块的下沉，(3)美国西部下地幔中较年轻、较晚俯冲的板块的下沉，以及(4)岩石圈的小规模对流滴下。得益于EarthScope，相关的深层结构最近被绘制到前所未有的细节；由此产生的地幔流的结果对于施加在岩石圈上的力以及地幔上升和减压引起的融化异常具有重要的地质意义。诱导流也很重要，因为它可以产生可观察到的预测，可以用作基于物理模型的约束，例如地震各向异性，以及大陆地壳的隆起和变形。项目分析方法包括将地幔的地震图像映射到密度结构中，然后用于驱动地幔流动的计算机模型。全球地震图像和流动模型用于解释大尺度过程，高分辨率地震图像和区域流动模型用于美国西部地下。EarthScope GPS数据提供了高分辨率的地壳应变率场，EarthScope远震数据提供了用于推断密度、温度和各向异性结构的详细地震图像。在寻找最能解释观测结果的模型时，探索了那些影响可解决约束的参数，从而提高了对诸如板块强度和机械行为等问题的理解。特别令人感兴趣的是：(1)大尺度流动模式与北美板块之间的耦合程度（特别强调深入软流层的克拉通根的影响）；(2)美国西部年轻板块下沉对黄石烟柱上升和区域尺度流动的重要性，这些流动可能集中在活跃的北部盆地和山脉省之下；(3)在美国西部许多年轻的隆起和火山场附近拍摄到的岩石圈水滴；(4)这些过程对地球长期的构造和热演化可能起的一般作用。

This project studies the causes and consequences of mantle flow beneath the western United States (U.S.). Several, interacting spatio-temporal scales of geologic activity need to be considered: (1) circulation related to North America plate motion, (2) sinking of old Farallon plate in the lower mantle beneath the eastern U.S., (3) sinking of younger, more recently subducted plate in the upper mantle beneath the western U.S., and (4) small-scale convective dripping of the lithosphere. Related deep structure has recently been mapped to unprecedented detail thanks to EarthScope; the consequences of the resulting mantle flow are geologically important for the forces applied to the lithosphere, and for melting anomalies caused by mantle ascent and decompression. Induced flow is also important because it results in observable predictions that can be used as a constraint for physics-based models, such as seismic anisotropy, and the uplift and deformation of the continental crust.The project analysis method involves mapping seismic images of the mantle into density structure that can then be used to drive computer models of mantle flow. Global seismic images and flow modeling are used to account for the large-scale processes, and high-resolution seismic images and regional flow modeling is used beneath the western U.S. EarthScope GPS data provide a highly resolved crustal strain-rate field and EarthScope teleseismic data provide detailed seismic images used to infer density, temperature, and anisotropy structure. Those parameters that affect resolvable constraints are explored in a search for the models that best account for the observations, leading to an improved understanding of issues such as the strength and mechanical behavior of plates.Of particular interest are: (1) the magnitude of coupling between the large-scale flow patterns and the North American plate (with special emphasis on the effects of a cratonic root that penetrates deeply into the asthenosphere); (2), the importance of the sinking young slab beneath western U.S. on Yellowstone plume ascent and regional-scale flow that may be concentrated beneath the active northern Basin and Range province; (3), the lithospheric drips that are imaged adjacent to many of the young western U.S. uplifts and volcanic fields, and, (4), the general role such processes may play for the long-term tectonic and thermal evolution of the Earth.