Age-independent seismic anisotropy under oceanic plates explained by strain history in the asthenosphere
Age-independent seismic anisotropy under oceanic plates explained by strain history in the asthenosphere
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软流圈应变历史解释大洋板块下与年龄无关的地震各向异性
DOI：
10.1016/j.epsl.2016.12.004
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发表时间：
2017
影响因子：
5.3
通讯作者：
Hedjazian N
中科院分区：
文献类型：
--
作者：
Hedjazian N
根据剪切波速度推断的大洋岩石圈-软流圈边界(LAB)的深度随着岩石圈年龄的增加而增加，这与大洋岩石圈冷却模型相一致。另一方面，大洋板块下方的径向各向异性分布几乎与年龄无关。特别是，径向各向异性在∼70公里处显示出最大正梯度，如果将其作为替代，则表示与年龄无关的实验室深度。这些截然不同的观察结果引发了关于该实验室地震学特征的争议。为了更好地理解这些观测之间的差异，我们模拟了上地幔晶体集合体中晶格择优取向(LPO)的发展，并预测了板块驱动的大洋中脊流动所产生的地震各向异性。该模型考虑了岩石圈随年龄的逐渐冷却，并考虑了扩散和位错蠕变变形机制。我们发现，径向各向异性的年龄无关分布是这些简单流动的自然结果。各向异性的深度和强度进一步由晶体在上升到脊轴以及随后远离脊轴的过程中经历的变形机制--位错或扩散蠕变--控制。与表面波层析成像模型相比，得到了诸如活化体积等流变学参数的约束。虽然不排除，但提出的解释实验室某些地球物理特征的额外机制，如部分熔体的存在或水分含量的变化，不需要解释径向各向异性代理。我们的预测，即与年龄无关的径向各向异性指标标志着向流动诱导的软流圈各向异性的转变，提供了一种协调实验室的热、力学和地震学观点的方法。
The depth of the oceanic lithosphere–asthenosphere boundary (LAB), as inferred from shear wave velocities, increases with lithospheric age, in agreement with models of cooling oceanic lithosphere. On the other hand, the distribution of radial anisotropy under oceanic plates is almost age-independent. In particular, radial anisotropy shows a maximum positive gradient at a depth of ∼70 km, which, if used as a proxy, indicates an age-independent LAB depth. These contrasting observations have fueled a controversy on the seismological signature of the LAB. To better understand the discrepancy between these observations, we model the development of lattice preferred orientation (LPO) in upper mantle crystal aggregates and predict the seismic anisotropy produced by plate-driven mid-ocean ridge flows. The model accounts for the progressive cooling of the lithosphere with age and can incorporate both diffusion and dislocation creep deformation mechanisms. We find that an age-independent distribution of radial anisotropy is the natural consequence of these simple flows. The depth and strength of anisotropy is further controlled by the deformation regime – dislocation or diffusion creep – experienced by crystals during their ascent towards, and subsequent motion away from, the ridge axis. Comparison to surface wave tomography models yield constraints on rheological parameters such as the activation volume. Although not excluded, additional mechanisms proposed to explain some geophysical signatures of the LAB, such as the presence of partial melt or changes in water content, are not required to explain the radial anisotropy proxy. Our prediction, that the age-independent radial anisotropy proxy marks the transition to flow-induced asthenospheric anisotropy, provides a way to reconcile thermal, mechanical and seismological views of the LAB.
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影响因子：
3.7
作者：
Y. Boneh;L. Morales;É. Kaminski;P. Skemer
通讯作者：
Y. Boneh;L. Morales;É. Kaminski;P. Skemer
部分熔融聚集体变形中各向异性邻接的发展：2. 对岩石圈-软流圈边界的影响
DOI：
--
发表时间：
2015
期刊：
影响因子：
--
作者：
S. Hier‐Majumder;T. Drombosky
通讯作者：
T. Drombosky
内在与外在地震各向异性：参考地球模型中的径向各向异性
DOI：
--
发表时间：
2013
期刊：
影响因子：
--
作者：
Nian Wang;J. Montagner;A. Fichtner;Y. Capdeville
通讯作者：
Y. Capdeville
影响因子：
5.3
作者：
Becker, Thorsten W.;Conrad, Clinton P.;Lebedev, Sergei
通讯作者：
Lebedev, Sergei
从长周期面波频散推断的太平洋地震各向异性*
DOI：
--
发表时间：
1985
期刊：
影响因子：
--
作者：
J. Montagner
通讯作者：
J. Montagner