Lowermost Mantle Anisotropy Beneath Africa From Differential SKS‐SKKS Shear‐Wave Splitting
Lowermost Mantle Anisotropy Beneath Africa From Differential SKS‐SKKS Shear‐Wave Splitting
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非洲下方最底层地幔各向异性的 SKS-SKKS 剪切波分裂差异
DOI：
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
N. Creasy
中科院分区：
文献类型：
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作者：
M. Reiss;M. Long;N. Creasy
利用SKS-SKKS差分剪切波分裂观测资料，研究了非洲大低速剪切带(LLSVP)附近地幔下部的地震各向异性。我们使用了来自非洲375个永久和临时站点的数据，这使我们能够以前所未有的详细程度绘制出最低地幔各向异性区域的空间分布。我们的结果证实了以前的发现，即在LLSVP的边缘观察到最明显的各向异性，表明其边界发生了强烈的变形，并且它们与LLSVP内部的基本各向同性是一致的。我们发现，大多数不一致的SKS-SKKS测量结果采样了最低的地幔，接近被推测为阿法尔羽流的根部。我们还在中非下方LLSVP底部先前绘制的超低速带(ULVZ)附近发现了强烈不一致的分裂。这代表了在空间上与ULVZ重合的下地幔各向异性的异常观测，并可能反映了一种独特的各向异性机制，如部分熔体的排列或强各向异性镁辉石的存在。我们将LLSVP以外的不一致测量解释为可能反映了流动方向从水平面向更垂直的方向的变化，这可能是由于LLSVP陡峭边界的偏转造成的。我们认为，我们观察到的与非洲LLSVP有关的D“各向异性可以用一种地幔流动机制来解释，该机制以板条驱动的被动热化学堆积为基础，并允许在其边缘形成上升流。
We investigate seismic anisotropy in the lowermost mantle in the vicinity of the African large low shear velocity province (LLSVP) using observations of differential SKS‐SKKS shear‐wave splitting. We use data from 375 permanent and temporary stations in Africa which enable us to map the spatial distribution of the anisotropic regions of the lowermost mantle in unprecedented detail. Our results corroborate previous findings that anisotropy is most clearly observed at the margins of the LLSVP, indicating strong deformation at its border, and they are generally consistent with a mostly isotropic LLSVP interior. We find that most discrepant SKS‐SKKS measurements sample the lowermost mantle close to what is inferred to be the root of the Afar plume. We also identify strongly discrepant splitting in the vicinity of a previously mapped ultralow velocity zone (ULVZ) at the base of the LLSVP, beneath Central Africa. This represents an unusual observation of lowermost mantle anisotropy that is spatially coincident with a ULVZ and may reflect a unique anisotropic mechanism such as alignment of partial melt or the presence of strongly anisotropic magnesiowüstite. We interpret discrepant measurements outside of the LLSVP as likely reflecting a change in flow direction from the horizontal plane to a more vertical direction, which may be caused by deflection at the steep LLSVP border. We propose that our observations of D″ anisotropy associated with the African LLSVP can be explained by a mantle flow regime that maintains passive thermochemical piles with slab‐driven flow and allows for the formation of upwellings at their edges.
DOI：
10.1002/2016jb013020
发表时间：
2016-09
期刊：
Journal of Geophysical Research: Solid Earth
影响因子：
--
作者：
M. Reiss;G. Rümpker;F. Tilmann;X. Yuan;J. Giese;E. Rindraharisaona
通讯作者：
M. Reiss;G. Rümpker;F. Tilmann;X. Yuan;J. Giese;E. Rindraharisaona
SplitRacer：用于远震剪切波分裂半自动分析和解释的 MATLAB 代码和 GUI
影响因子：
3.3
作者：
Rümpker
通讯作者：
Rümpker