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

合作研究：美国西部地下上地幔异质性成像的地球动力学意义

• 批准号: 0911006
• 负责人: Eugene Humphreys
• 金额: $ 4.06万
• 依托单位: University of Oregon Eugene
• 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 2011-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911006&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。需要考虑几个相互作用的地质活动时空尺度：(1)与北美板块运动有关的环流，(2)旧的Farallon板块在美国东部下地幔下沉，(3)较新的新俯冲板块在美国西部下地幔下沉，以及(4)岩石圈的小规模对流滴落。多亏了地球望远镜，相关的深部结构最近被绘制成了前所未有的细节；由此产生的地幔流动的后果对于施加到岩石圈的力以及地幔上升和减压造成的融化异常具有重要的地质意义。诱发流动也很重要，因为它产生了可用于约束基于物理的模型的可观测预测，例如地震各向异性以及大陆地壳的抬升和变形。项目分析方法涉及将地幔的地震图像映射到密度结构，然后可用于驱动地幔流动的计算机模型。全球地震图像和流动模拟被用来解释大范围的过程，高分辨率地震图像和区域流动模拟被用于美国西部地下。Earthscope GPS数据提供了高分辨率的地壳应变率场，而EarthScope远程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。对那些影响可分辨约束的参数进行了探索，以寻找最能解释观测的模型，从而提高了对板块强度和力学行为等问题的理解。特别感兴趣的是：(1)大尺度流动模式和北美板块之间的耦合程度(特别强调深入软流圈的克拉通根部的影响)；(2)美国西部下方下沉的年轻板块对黄石羽流上升和可能集中在活跃的北部盆地和山脉省以下的区域尺度流动的重要性；(3)在许多年轻的美国西部隆起和火山田附近拍摄到的岩石圈水滴，以及(4)这些过程对地球长期构造和热演化可能起到的一般作用。