Collaborative Research: Investigating Temperature, Melting, and Mantle Flow in the North American Upper Mantle with 3-D Models of Shear Velocity, Radial Anisotropy, and Attenuation

合作研究：利用剪切速度、径向各向异性和衰减的 3D 模型研究北美上地幔的温度、熔化和地幔流动

• 批准号: 1252039
• 负责人: James Gaherty
• 金额: $ 10.29万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-03-15 至 2016-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1252039&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; Temperature; Melting

The continent of North America is geologically and tectonically diverse. The western half of the continent includes a major plate boundary and has been host to mountain-building events, volcanism, and extension within the recent geological past. The eastern portion of North America is located far from any plate boundary and has not experienced significant tectonic activity in hundreds of millions of years. Understanding how the dynamic processes occurring in Earth's interior have given rise to this complex terrain is fundamental to understanding the growth and evolution of continents in general and North America in particular. Imaging variations in the speed of seismic waves traveling through the crust and mantle provides important constraints on the temperature and composition of those regions as well as the presence of partially molten rock. However, since each of these factors, and any combination of them, can affect velocity, additional data sets are needed to achieve a robust interpretation. The absorption of seismic-wave energy is also controlled by temperature, composition, and melt content, and thus jointly interpreting variations in seismic-wave velocity and attenuation allows for improved constraints on the properties of Earth's interior. To date, there have been very few studies of seismic attenuation beneath North America, largely because of the difficulties involved with measuring and analyzing the amplitudes of seismic waves. The PIs will develop 3-D models of shear attenuation and radially anisotropic shear velocity for the North American upper mantle using surface waves recorded by USArray. Surface-wave phase and amplitude are measured using a new interstation cross-correlation approach that exploits waveform similarity at nearby stations, and the phase and amplitude data will be utilized together to take advantage of the dependence of both data sets on seismic velocity and attenuation. From these models, variations in temperature, composition, and partial melt across the continent will be estimated, and a more complete picture of how structures like the Colorado Plateau, the Basin and Range, the Mid-Continent Rift, and the North American craton are controlled by the processes in and properties of the underlying mantle will emerge.

北美大陆的地质和构造多种多样。非洲大陆的西半部有一个主要的板块边界，在最近的地质历史中曾发生过造山活动、火山活动和扩张。北美东部远离任何板块边界，数亿年来没有经历过重大的构造活动。了解地球内部发生的动态过程如何产生这种复杂的地形对于了解整个大陆（尤其是北美）的生长和演化至关重要。穿过地壳和地幔的地震波速度的成像变化为这些区域的温度和成分以及部分熔融岩石的存在提供了重要的限制。然而，由于这些因素中的每一个以及它们的任意组合都会影响速度，因此需要额外的数据集来实现可靠的解释。 地震波能量的吸收也受到温度、成分和熔体含量的控制，因此共同解释地震波速度和衰减的变化可以改善对地球内部特性的限制。迄今为止，对北美地下地震衰减的研究很少，主要是因为测量和分析地震波振幅存在困难。 PI 将使用 USArray 记录的表面波开发北美上地幔剪切衰减和径向各向异性剪切速度的 3D 模型。使用新的站间互相关方法测量表面波相位和振幅，该方法利用附近站的波形相似性，并且相位和振幅数据将一起利用，以利用两个数据集对地震速度和衰减的依赖性。根据这些模型，将估计整个大陆的温度、成分和部分融化的变化，并更全面地了解科罗拉多高原、盆地和山脉、中大陆裂谷和北美克拉通等结构的变化情况。由底层地幔的过程和特性控制的将会出现。