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

对岩石圈结构的详细地震调查将检验关于加州南部大峡谷上地幔伊莎贝拉高地震速度异常构造起源的两个假说。根据现有的地震成像，这两种假设都是可行的，这些地震成像使用的是相距约70公里的台站的数据，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。另一种将伊莎贝拉异常归因于化石板块，该板块是蒙特利微板块在大峡谷下方连贯平移的延续，因为它与太平洋板块机械耦合。重要的是，后一种假设将化石板块置于圣安德烈亚斯断层段沿走向范围的下方，该断层段主要通过非地震蠕变变形，并存在地壳深层构造震动，这可能是由板块的流体引起的。使用从海岸延伸到内华达山脉山麓的密集宽带阵列的被动震源地震成像将有力地检验这两个假设，详细绘制岩石圈界面，并识别它们是否连续穿过累积右端位移为300公里的板块边界断层。散射波偏移和层析成像方法将结合使用，以约束密集阵列下的岩石圈结构。地震研究将促进对俯冲终止的构造遗产和力学、内华达山脉岩石圈的俯冲后演化以及圣安德烈亚斯断层蠕动段现今的基本边界条件的理解。科学进步的明确机会不仅是因为对基本构造过程的潜在影响，而且是因为存在两个关于岩石圈规模结构的明确假设，可以用现代被动震源地震成像方法进行强有力的检验。该项目的其他影响包括帮助新墨西哥大学(UNM)发展一个新的地球物理学小组，支持一名开始职业生涯的PI、一名研究生和一名本科生研究员。新墨西哥州的地球物理研究和教学的扩展？S最大的机构具有突出的潜力，吸引未被充分代表的少数族裔获得地球科学的机会。加州理工学院将资助一名研究生和本科生研究员。该项目将在新墨西哥州大学和加州理工学院之间发展一种新的合作。

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.