New Insights into the Fine-scale Behavior of Subducted Slab Around the Transition Zone and in the Deep Mantle

对过渡带周围和地幔深部俯冲板块精细尺度行为的新见解

• 批准号: 0842753
• 负责人: Jun Korenaga
• 金额: $ 26.68万
• 依托单位: Yale University
• 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: 2009-01-01 至 2011-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0842753&HistoricalAwards=false
• 关键词: New; Insights; into; Fine; scale

The formation and evolution of the North American continent is characterized by the assembly and dispersal of smaller continental masses over the last three billion years. Understanding the origin of this continent thus provides important clues to long-term mantle dynamics, and by the same token, understanding the global framework of mantle dynamics is vital to properly interpret fragmentary geological records and assimilate them into a unifying model for continental evolution. This project hinges on the notion that substantial progress in a regional perspective would be achieved most efficiently if concurrent development is also made in a global framework, and is motivated by a unique and exciting opportunity provided by the USArray to make considerable progress toward resolving first-order issues such as the structure of mantle convection and its chemical evolution. The style of mantle convection has been debated intensely in the last few decades, and migration imaging has a potential to make a breakthrough, by providing a new kind of seismic evidence complementary to tomographic imaging. Subducted slab is not only cooler than the ambient mantle but also composed of two chemically distinct layers, namely thin garnet-rich oceanic crust and olivine-rich mantle lithosphere. The thermal signature of subducted slab becomes more difficult to detect in the deep mantle because seismic velocity becomes less sensitive to temperature with increasing pressures, but its chemical signature remains robust, which may be detected by analyzing seismic array data. Also, mantle differentiation responsible for the chemical layering of subducted slabs points to another important role played by migration imaging in understanding chemical geodynamics, namely the seismic mapping of the fate of subducted oceanic crust. In order to advance our understanding on the style of mantle convection and its chemical evolution, the PI and his colleague apply new-generation migration methods to the USArray data to image the three-dimensional distribution of fine-scale scatterers throughout the mantle beneath Central America. Central America is one of the few regions where subducted slab seems to penetrate into the lower mantle according to a number of tomographic models, and it is well situated in terms of the distribution of seismic sources and receivers, i.e., deep-focused earthquakes in South America and a large-aperture seismic array in North America (USArray). This research is also coupled with undergraduate education, by designing a new laboratory session for a core course in geophysics and recruiting students to array seismology data processing. The source code of the advanced migration methods is planned to be distributed, together with a user manual and a tutorial.

北美大陆的形成和演变的特征是在过去三十亿年中大陆群体的大陆群众集会和散布。因此，了解该大陆的起源为长期地幔动力学提供了重要的线索，并且通过同样的标记，了解地幔动态的全球框架对于正确解释碎片地质记录并将其吸收成大陆进化的统一模型至关重要。该项目取决于这样的观念，即如果在全球框架中也进行并发发展，将最有效地取得最有效的进展，并以USArray提供的独特而激动人心的机会来激励，以在解决一阶问题（例如Mantle Contrection及其化学进化的结构）方面取得相当大的进步。在过去的几十年中，对对流的风格进行了激烈的辩论，而迁移成像具有通过提供一种新型的地震证据互补的层压成像，有可能取得突破。俯冲板不仅比环境地幔凉爽，而且还由两个化学上不同的层组成，即富含石榴石的海洋壳和富含橄榄石富含橄榄石的地幔岩石圈。俯冲平板的热特征在深套中变得更难检测到，因为地震速度随着压力的增加而对温度敏感不那么敏感，但是其化学签名仍然稳健，可以通过分析地震阵列数据来检测到。同样，俯冲板的化学分层的地幔分化表明，迁移成像在理解化学地球动力学方面起着另一个重要作用，即俯冲的海洋壳命运的地震映射。为了促进我们对地幔对流风格及其化学演化风格的理解，PI和他的同事将新一代迁移方法应用于USArray数据，以对中美洲下面的地幔的三维散射器的三维分布进行想象。中美洲是俯冲板似乎根据许多层析成像模型渗透到较低地幔中的少数地区之一，并且它位于地震来源和接收器的分布方面，即南美洲的深层地震，即北美地区的大量地震阵列（USArray）。这项研究还与本科教育一起设计了一个新的实验室课程，用于地球物理学的核心课程，并招募学生进行阵列地震学数据处理。计划分发高级迁移方法的源代码以及用户手册和教程。