Mantle Flow in the Vicinity of the Eastern Edge of the Pacific‐Yakutat Slab: Constraints From Shear Wave Splitting Analyses
Mantle Flow in the Vicinity of the Eastern Edge of the Pacific‐Yakutat Slab: Constraints From Shear Wave Splitting Analyses
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DOI：
10.1029/2021jb022354
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发表时间：
2021-09
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影响因子：
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通讯作者：
Yuchen Yang;Stephen S. Gao;Kelly H. Liu;F. Kong;Xiaofei Fu
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作者：
Yuchen Yang;Stephen S. Gao;Kelly H. Liu;F. Kong;Xiaofei Fu
为了研究板片边缘和变化的板片几何形状对阿拉斯加中南部下方地幔流系统的影响，使用来自 USArray 和其他网络的数据测量了总共 971 对远震剪切波（SKS、SKKS 和 PKS）和 65 对局部 S 波分裂参数（快速方向和分裂时间）。太平洋-雅库塔特板块边缘将两个具有不同分裂测量特征的区域分开。板片边缘以西的区域劈裂次数较多，且多为沟槽平行的快速取向，而以东区域则以较小的劈裂次数和空间变化的快速取向为主。分裂参数的空间分布以及各向异性分层和深度分析的结果可以通过涉及三个流动系统的模型来解释。由于板片后退和板片倾角增加，最初夹带浅倾角雅库塔特板片的下板片流偏转至与沟槽平行的方向，并向东北流向板片边缘，并在此处分裂成两个分支。第一个分支作为环形流进入地幔楔，并沿着板片向西南流动，第二个分支继续大致向东流动。环形流和连续流系统的流线在板边缘附近近似彼此正交，产生观察到的小分裂时间和空间变化的快速方向。
To investigate the effects of a slab edge and varying slab geometry on the mantle flow systems beneath south central Alaska, a total of 971 pairs of teleseismic shear wave (SKS, SKKS, and PKS) and 65 pairs of local S wave splitting parameters (fast orientations and splitting times) are measured using data from the USArray and other networks. The Pacific‐Yakutat slab edge separates two regions with different characteristics of the splitting measurements. The area to the west of the slab edge has greater splitting times and mostly trench parallel fast orientations, and the area to the east is dominated by smaller splitting times and spatially varying fast orientations. The spatial distribution of the splitting parameters and results of anisotropy layering and depth analyses can be explained by a model involving three flow systems. The sub‐slab flow initially entraining with the shallow‐dipping Yakutat slab deflects to a trench‐parallel direction due to slab retreat and an increase in slab dip, and flows northeastward toward the slab edge, where it splits into two branches. The first branch enters the mantle wedge as a toroidal flow and flows southwestward along the slab, and the second branch continues approximately eastward. The flowlines of the toroidal and continued flow systems are approximately orthogonal to each other in the vicinity of the slab edge, producing the observed small splitting times and spatially varying fast orientations.