Investigating ultra-low velocity zones in the southern hemisphere using an Antarctic dataset
Investigating ultra-low velocity zones in the southern hemisphere using an Antarctic dataset
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DOI：
10.1016/j.epsl.2020.116142
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发表时间：
2020-04-15
影响因子：
5.3
通讯作者：
Yu, Shule
中科院分区：
文献类型：
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作者：
Hansen, Samantha E.;Carson, Sarah E.;Yu, Shule
考虑到最低地幔的地震覆盖范围有限，只有不到五分之一的核心-地幔边界（CMB）被调查了超低速度带（ULVZs）的存在。因此，以新的几何形状对CMB进行采样的研究对于进一步了解ULVZ的起源及其与其他地球深部过程的潜在联系非常重要。利用最近部署在南极洲的南极横贯山脉北部网络记录的核心反射ScP波，目前的研究旨在扩大南半球的ULVZ调查。我们的数据集对新西兰附近的CMB进行了采样，提供了东北地区的覆盖范围，此前已经确定了ULVZ结构，而南部的另一个地区先前的ULVZ证据尚无定论。该地区的数据样本横跨太平洋大低剪切速度省（LLSVP）的边界，因此特别令人感兴趣。南极洲附近的威德尔海地区也有很好的样本，为以前没有研究过的地区提供了新的信息。大型一维合成地震记录数据库与ScP观测数据的关联方案表明，两个研究区域都需要ulvz。建模的不确定性限制了我们明确定义超空速特性的能力，但也可能表明更复杂的三维结构。考虑到ulvz是在太平洋LLSVP内部、边缘和远离LLSVP的地方检测到的，我们的结果支持了ulvz在成分上与周围地幔不同的假设，并且不仅仅与部分熔融有关。ulvz可能在CMB中无处不在；然而，它们在许多区域可能比目前的方法更薄。在某些地区，地幔对流可能会将ulvz扫成更厚的堆，将这些异常推向llsvp的边界。(C) 2020作者。Elsevier B.V.出版
Given limited seismic coverage of the lowermost mantle, less than one-fifth of the core-mantle boundary (CMB) has been surveyed for the presence of ultra-low velocity zones (ULVZs). Investigations that sample the CMB with new geometries are therefore important to further our understanding of ULVZ origins and their potential connection to other deep Earth processes. Using core-reflected ScP waves recorded by the recently deployed Transantarctic Mountains Northern Network in Antarctica, the current study aims to expand ULVZ investigations in the southern hemisphere. Our dataset samples the CMB in the vicinity of New Zealand, providing coverage between an area to the northeast, where ULVZ structure has been previously identified, and another region to the south, where prior evidence for a ULVZ was inconclusive. This area is of particular interest because the data sample across the boundary of the Pacific Large Low Shear Velocity Province (LLSVP). The Weddell Sea region near Antarctica is also well sampled, providing new information on a region that has not been previously studied. A correlative scheme between a large database of 1-D synthetic seismograms and the observed ScP data demonstrates that ULVZs are required in both study regions. Modeling uncertainties limit our ability to definitively define ULVZ characteristics but also likely indicate more complex 3-D structure. Given that ULVZs are detected within, along the edge of, and far from the Pacific LLSVP, our results support the hypothesis that ULVZs are compositionally distinct from the surrounding mantle and are not solely related to partial melt. ULVZs may be ubiquitous along the CMB; however, they may be thinner in many regions than can be resolved by current methods. Mantle convection currents may sweep the ULVZs into thicker piles in some areas, pushing these anomalies toward the boundaries of LLSVPs. (C) 2020 The Author(s). Published by Elsevier B.V.