Mineralogy, fabric and deformation domains in D? across the southwestern border of the African LLSVP
Mineralogy, fabric and deformation domains in D? across the southwestern border of the African LLSVP
复制标题
D 中的矿物学、织物和变形领域？
DOI：
10.1093/gji/ggac359
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发表时间：
2023
影响因子：
2.8
通讯作者：
Pisconti A
中科院分区：
文献类型：
--
作者：
Pisconti A
地震各向异性研究的最新进展，联合使用反射和剪切波分裂已被证明放置在D″区的合理的各向异性和变形的情况下，严格的约束。我们将这种新的方法应用于南大西洋下的D″区域的大面积区域，该区域靠近非洲大型低地震速度区（LLSVP）。这一地区的地幔的特点是从快速到缓慢的地震速度异常的过渡，它被认为是负责热点火山活动的深层羽流的位置。试图探测地幔成分和变形沿着LLSVP边界可能提供地幔动力学的关键信息。通过对该地区地震相采样的分析，我们在南大西洋下的一大片区域探测到了一个D″不连续面，推断深度范围为核幔边界以上170 ~ 240 km。我们在LLSVP区域内发现了D″反射体的证据。剪切波分裂观测表明，各向异性是存在于该地区的地幔，与以前的研究，部分采样该地区。我们模拟观察到的晶格和形状优选取向的材料预期在D″区域。解释这些数据需要矿物学、相变边界和变形方向的区域变化。我们推断两个不同的域的矿物学和变形：对齐后钙钛矿外的LLSVP和对齐bridgmanite内的LLSVP。本研究所描绘的情景与LLSVP组成的当前假设以及预期沿沿着LLSVP边界发生的垂直变形方向的普遍性一致。
Recent advances in seismic anisotropy studies that jointly use reflections and shear wave splitting have proven to place tight constraints on the plausible anisotropic and deformation scenarios in the D″ region. We apply this novel methodology to a large area of the D″ region beneath the South Atlantic, in proximity to and within the African large low seismic velocity province (LLSVP). This area of the mantle is characterized by a transition from fast to slow seismic velocity anomalies and it is thought to be the location of deep-seated plumes responsible for hotspot volcanism. Attempting to probe mantle composition and deformation along the LLSVP borders may provide key information on mantle dynamics. By analysing seismic phases sampling this region, we detect a D″ discontinuity over a large area beneath the South Atlantic, with inferred depth ranges ∼170 to ∼240 km above the core–mantle boundary. We find evidence for a D″ reflector within the area of the LLSVP. Shear wave splitting observations suggest that anisotropy is present in this region of the mantle, in agreement with previous studies that partially sampled this region. We model the observations considering lattice- and shape-preferred orientation of materials expected in the D″ region. A regional variation of mineralogy, phase transition boundaries, and deformation direction is required to explain the data. We infer two distinct domains of mineralogy and deformation: aligned post-perovskite outside the LLSVP and aligned bridgmanite within the LLSVP. The scenario depicted by this study agrees well with the current hypotheses for the composition of the LLSVP and with the prevalence of vertical deformation directions expected to occur along the LLSVPs borders.