Collaborative Research: Is the Isabella anomaly a fossil slab or the foundered lithospheric root of the Sierra Nevada batholith?

合作研究：伊莎贝拉异常是一块化石板还是内华达山脉基岩沉没的岩石圈根部？

• 批准号: 1314910
• 负责人: Robert Clayton
• 金额: $ 13.65万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-15 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1314910&HistoricalAwards=false
• 关键词: Collaborative; Research; Isabella; anomaly; fossil

A detailed seismic investigation of lithospheric structure will test two hypotheses for the tectonic origin of the Isabella high seismic velocity anomaly in the upper mantle of California's southern Great Valley. Both hypotheses are viable based on existing seismic imaging that uses data from stations spaced about 70 km apart, but they have dramatically different implications for the processes that accompany subduction termination and the evolution of continental arc lithosphere. One hypothesis attributes the Isabella Anomaly to the sinking mafic root of the southern Sierra Nevada batholith. The other attributes the Isabella Anomaly to a fossil slab that is a continuation of the Monterey microplate coherently translating beneath the Great Valley because it is mechanically coupled to the Pacific plate. Importantly, the latter hypothesis places the fossil slab beneath the along-strike extent of the section of the San Andreas fault that dominantly deforms by aseismic creep and hosts deep crustal tectonic tremor, which might be caused by fluids from the slab. Passive source seismic imaging using a dense broadband array with ~7 km station spacing extending from the coast to the Sierra Nevada foothills will robustly test the two hypotheses with detailed mapping of lithospheric interfaces and identification of whether or not they are continuous across a plate bounding fault with 300 km of cumulative right lateral displacement. Scattered wave migration and tomographic imaging methods will be used in concert to constrain lithospheric structure beneath the dense array. The seismic study will advance understanding of the structural legacy and mechanics of subduction termination, post-subduction evolution of the Sierra Nevada arc lithosphere, and present day basal boundary conditions on the creeping section of the San Andreas fault. A clear opportunity for scientific advance is identified not only by the potential implications for fundamental tectonic processes, but also by the existence of two well-defined hypotheses for lithospheric-scale structure that can be robustly tested with modern passive source seismic imaging methods. Additional impacts of the project include aiding in the development of a new geophysics group at the University of New Mexico (UNM) by supporting a beginning-career PI, a graduate student, and an undergraduate researcher. Expansion of geophysics research and teaching at the state of New Mexico?s largest institution has outstanding potential to attract under-represented minorities to opportunities in the geosciences. A graduate student and undergraduate researcher will be supported at Caltech. The project will develop a new collaboration between UNM and Caltech.

对岩石圈结构的详细地震调查将检验关于加利福尼亚州南部大峡谷上地幔伊莎贝拉高地震速度异常的构造起源的两种假设。基于现有的地震成像，这两种假设都是可行的，现有的地震成像使用了相距约 70 公里的台站数据，但它们对伴随俯冲终止和大陆弧岩石圈演化的过程有着截然不同的影响。一种假设将伊莎贝拉异常归因于内华达山脉南部岩基下沉的镁铁质根部。另一种说法将伊莎贝拉异常归因于一块化石板，该化石板是蒙特雷微板块的延续，由于它与太平洋板块机械耦合，因此在大峡谷下方一致平移。重要的是，后一种假设将化石板块置于圣安德烈亚斯断层部分的沿走向范围之下，该断层主要因抗震蠕变而变形，并发生深层地壳构造震动，这可能是由板块中的流体引起的。使用从海岸延伸到内华达山脉山麓的密集宽带阵列（站间距约为 7 公里）的被动源地震成像将通过详细绘制岩石圈界面并识别它们是否在板块边界断层上连续来有力地检验这两个假设累计右侧横向位移 300 公里。将结合使用散射波偏移和断层扫描成像方法来约束密集阵列下方的岩石圈结构。地震研究将加深对俯冲终止的结构遗产和力学、内华达山脉弧岩石圈俯冲后演化以及圣安德烈亚斯断层蠕变部分当今基底边界条件的理解。科学进步的明显机会不仅来自于对基本构造过程的潜在影响，还来自于岩石圈尺度结构的两个明确的假设的存在，这些假设可以用现代被动源地震成像方法进行可靠的测试。该项目的其他影响包括通过支持一名刚开始职业生涯的 PI、一名研究生和一名本科生研究员来帮助新墨西哥大学 (UNM) 发展一个新的地球物理学小组。新墨西哥州最大机构的地球物理学研究和教学的扩展具有吸引代表性不足的少数群体获得地球科学机会的巨大潜力。加州理工学院将支持一名研究生和本科生研究员。该项目将在新墨西哥大学和加州理工学院之间建立新的合作关系。