Mantle volatiles and attenuation in the East African Rift

东非裂谷之下的地幔是在地球上地幔中观察到的最显著的地球物理异常之一，其特征是地震波速非常低的广阔区域。尽管地幔温度的升高可能会减缓地震波的速度，但来自喷发的熔岩成分的限制表明，该地区的地幔是温暖的，但还没有热到足以解释观测到的地震波的最大慢速。地幔中挥发性元素(如水、碳)浓度的升高也会减缓地震波的速度，但对东非裂谷沿线的地幔来说，这是不受限制的。定量该地区地幔中水和碳的丰度对于描述沿裂谷长度发生的岩浆作用及其与裂谷本身的过程的关系至关重要。此外，协调该地区地幔的地球物理和地球化学模型是对目前更广泛地了解地球地幔的关键考验。这项工作将综合现有样本集和地球物理数据集收集的信息，为未来的实地和实验活动提供信息。除了科学影响，这项工作扩大了代表不足的群体的参与，并支持了几名本科生和研究生。这项工作还将为加州大学河滨分校(UCR)地球科学博物馆的一个展览提供信息。如果地幔明显富含水或碳，这可能会导致地幔在更高的压力和更低的温度下融化，而不是干燥的无碳地幔。熔体的存在也可能减慢地震波的速度。这项工作将限制个别火山建筑物的地幔来源挥发分组成，并评估挥发分、温度和熔融升高对裂谷下地球物理异常极端性质的重要性，以及对裂谷本身的启动和演化的重要性。这项工作将测试该地区地幔的岩石学描述和地震波特性之间的现有定量关系。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The mantle under the East African Rift features one of the most prominent geophysical anomalies observed in Earth's upper mantle, defined by a broad region of very low seismic wave speeds. Though increased mantle temperatures could slow seismic wave speeds, constraints from erupted lava compositions indicate that the mantle in this region is warm, but not hot enough to account for the observed maximum slowness of seismic waves. Elevated concentrations of volatile elements (e.g., water, carbon) in the mantle can also slow seismic wave speeds, but these are unconstrained for the mantle along the East African Rift. Quantifying the abundance of water and carbon in the mantle in this region is critical to describing the magmatism that has occurred along the length of the rift, and its relationship to the process of rifting itself. Additionally, reconciling geophysical and geochemical models for the mantle in this region is a key test of the current understanding of Earth's mantle more broadly. This work will inform future field and experimental campaigns by presenting a synthesis of information that can be gleaned by existing sample sets and geophysical data sets. In addition to the scientific impacts, this work broadens the participation of underrepresented groups and supports several undergraduate and graduate students. This work will also inform an exhibit for the University of California-Riverside (UCR) Earth Sciences Museum.If the mantle is significantly water- or carbon-rich, this could lead to mantle melting at higher pressures and lower temperatures than for a dry and carbon-free mantle. The presence of melts may also slow seismic wave speeds. This work will constrain the mantle source volatile composition at individual volcanic edifices and assess the importance of elevated volatiles, temperatures, and melts on the extreme nature of the geophysical anomaly under the rift, and to the initiation and evolution of the rift itself. This work will test existing, quantitative relationships between petrological descriptions of the mantle and the properties of seismic waves in this region.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.