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

合作研究：美国西部地区上地幔异质性成像的地球动力学意义

• 批准号: 0910985
• 负责人: Thorsten Becker
• 金额: $ 15.61万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0910985&HistoricalAwards=false
• 关键词: Collaborative; Research; Geodynamic; implications; imaged

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.

该项目研究美国西部地幔流动的原因和后果。需要考虑地质活动的几个相互作用的时空尺度：（1）与北美板块运动有关的环流，（2）美国东部下地幔中旧法拉隆板块的下沉，(3)在美国西部下的上地幔中，更年轻、更近的俯冲板块下沉，（4）岩石圈小尺度对流滴注。由于EarthScope，相关的深部结构最近被绘制成前所未有的细节;由此产生的地幔流动的后果对于施加在岩石圈上的力以及地幔上升和减压引起的熔融异常具有地质学意义。诱导流也很重要，因为它可以产生可观测的预测，这些预测可以用作基于物理模型的约束，例如地震各向异性和大陆地壳的隆起和变形。项目分析方法涉及将地幔的地震图像映射到密度结构，然后可以用于驱动地幔流的计算机模型。全球地震图像和流动模型被用来解释大规模的过程，高分辨率地震图像和区域流动模型被用于美国西部以下的EarthScope GPS数据提供了一个高分辨率的地壳应变率场和EarthScope地震数据提供了详细的地震图像，用于推断密度，温度和各向异性结构。这些影响可解析约束的参数在寻找最能解释观测结果的模型中进行了探索，从而提高了对板的强度和力学行为等问题的理解。特别感兴趣的是：（1）大尺度流型与北美板块之间的耦合程度（特别强调深入软流圈的超声波根的影响）;（二）、美国西部下方下沉的年轻板块对黄石火山柱上升和区域的重要性-可能集中在活跃的北方盆地和山脉省之下的尺度流动;（3）在美国西部许多年轻的隆起和火山区附近成像的岩石圈滴液;（4）这些过程可能对地球长期构造和热演化起的一般作用。