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

超低速带（ULVZ）是位于地幔最下部某些区域的薄（~10 km）层，位于与外核的边界上方，其特征是地震波速度急剧降低。 波速降低的原因尚不确定，但可能包括地幔熔融和地幔中的硅酸盐矿物与地核中的铁反应产生的化学不均匀性。 以前，低分辨率的研究表明ULVZ的地理范围暗示了大的区域斑块，然而，最近，由该小组成员进行的高分辨率观测揭示了一个可能比最初认为的更小规模的结构。 一个小的，孤立的口袋更密集的ULVZ材料被发现在一个区域，以前被认为包含一个更大的，连续的ULVZ层。 这里提出的工作涉及亚利桑那州立大学和加州伯克利大学的地震学家、数值和实验室地球动力学家的合作。 这项工作的最终目标是要确定如何从核幔边界的上涌地幔柱影响的局部几何形状的ULVZ，和一个令人兴奋的可能性，检查是否地震检测口袋的ULVZ可以被用作标记，以确定源区几乎地震不可见的地幔柱。 在地震学方面，将以比以前高得多的分辨率研究ULVZ，目的是确定以前认为连续的ULVZ区域是否由更密集区域的孤立口袋组成。 地球动力学，数值和实验室实验将被用来确定是否观察到的孤立的口袋ULVZ材料有关的地幔柱，如果是这样，什么是ULVZ材料的形态和流动模式与地幔柱源区之间的关系？ 最后，拟议的工作将集中在确定是否可以使用动态预测和观测的约束条件，以区分竞争的假设部分熔化和化学异质性的ULVZ的原因。

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.