CSEDI Collaborative Research: Investigating the Relationship Between Plume Dynamics and ULVZ Geometry

超低速带(ULVZ)是位于地幔下部与外核交界处正上方的薄层(~10公里)，其特征是地震波速急剧降低。波速降低的原因尚不清楚，但可能的可能性包括地幔小度熔融，以及地幔中的硅酸盐矿物与地核中的铁发生反应而产生的化学不均质性。以前，以ULVZ地理范围为特征的较低分辨率的研究暗示了大的区域斑块，然而，该小组成员最近进行的较高分辨率的观测揭示了一个潜在的较小规模的结构，而不是最初认为的。在之前被认为包含更大的、连续的ULVZ层的区域中，发现了一个小的、孤立的、密度更高的ULVZ物质。这里提出的工作涉及亚利桑那州立大学和加州大学伯克利分校的地震学家以及数值和实验室地球动力学专家的合作。这项工作的最终目标是确定源自核-地幔边界的上升地幔热柱如何影响ULZ的局部几何结构，一个令人兴奋的可能性是，ULZ的地震可探测区域是否可以用作标记，以确定地震上几乎看不见的地幔热柱的源区。在地震学方面，将以比以前高得多的分辨率研究ULZ，目的是确定以前认为连续的ULZ区域是否由更密集的孤立区域组成。将利用地球动力学、数值和实验室实验来确定观察到的ULVZ物质的孤立区域是否与地幔热柱有关，如果是，ULVZ物质的形态与与地幔热柱源区有关的流动模式之间的关系是什么？最后，拟议的工作将侧重于确定动态预测和观测约束是否可以用于区分部分熔化和化学不均匀作为ULVZ原因的相互竞争的假说。

The ultra-low velocity zone (ULVZ) is a thin ( ~10 km) layer in some regions of the lower-most mantle immediately above the boundary with the outer core that is characterized by a dramatic reduction in seismic wave speeds. The cause of this reduction in wave speed is uncertain, but likely possibilities include a small degree of mantle melting and chemical heterogeneity created by reactions between silicate minerals in the mantle with iron in the core. Previous, lower resolution studies that characterized the geographic extent of the ULVZ have hinted at large regional patches, however, recent, higher resolution observations made by members of this group have revealed a potentially smaller-scale structure than originally thought. A small, isolated pocket of more-dense ULVZ material was discovered in a region that was previously thought to contain a much larger, continuous ULVZ layer. Work proposed here involves a collaboration of seismologists and both numerical and laboratory geodynamicists at Arizona State University and the University of California Berkeley. The ultimate goal of this work is to determine how upwelling mantle plumes originating from the core-mantle boundary affect the local geometry of the ULVZ, and one exciting possibility to examine is whether seismically detectable pockets of ULVZ can be used as markers to determine the source region for nearly seismically-invisible mantle plumes. On the seismology front, the ULVZ will be studied at much higher resolution than before with the goal of determining whether previously-thought-continuous ULVZ regions are instead composed of isolated pockets of more-dense regions. Geodynamically, numerical and laboratory experiments will be used to determine whether observed isolated pockets of ULVZ material are related to mantle plumes, and if so, what is the relationship between the morphology of ULVZ material and the flow patterns associated with mantle plume source regions? Finally, proposed work will focus on determining whether the dynamically-predicted and observational constraints can be used to differentiate between competing hypotheses of partial melting and chemical heterogeneity as a cause of the ULVZ.