Variability and origin of seismic anisotropy across eastern Canada: Evidence from shear wave splitting measurements
Variability and origin of seismic anisotropy across eastern Canada: Evidence from shear wave splitting measurements
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加拿大东部地震各向异性的变化和起源：剪切波分裂测量的证据
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
B. Schow
中科院分区：
文献类型：
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作者：
F. Darbyshire;I. Bastow;A. Forte;T. Hobbs;A. Calvel;A. Gonzalez‐Monteza;B. Schow
在大陆地区的地震各向异性的测量经常解释相对于过去的构造过程，保存在岩石圈的“化石”组构。现今的岩石圈下流动模型（通常使用绝对板块运动作为替代）也被用来解释观测结果。区分这些不同的地震各向异性源在地盾下特别具有挑战性，其厚（≥200 km）的岩石圈根可能记录了长期的变形历史，并强烈影响底层地幔流动。加拿大东部的地质记录跨越了地球历史的1.3亿年，是解决这一问题的理想地区。我们使用剪切波分裂测量的核心阶段，如SKS定义上地幔各向异性使用的快速偏振方向的取向和延迟时间之间的快速和缓慢的剪切波到达δt。与地表地质和航磁资料中的构造趋势相比较，有助于确定化石岩石圈组构对各向异性的贡献。我们还通过全球地球动力学模型得出的流动方向来评估岩石圈下地幔流动的影响。整个区域的快极化方向通常为ENE-WSW到ESE-WNW，但在≤100 km尺度上分裂参数的显著横向变化意味着岩石圈对结果的贡献。然而，与构造地质和磁性趋势的相关性并不普遍，与地球动力学预测的地幔流动方向的相关性也不普遍。因此，我们认为分裂参数可能记录了现今地幔流和更古老的岩石圈组构的组合。在屏蔽区解释分裂观测时，考虑两种各向异性源是至关重要的。
Measurements of seismic anisotropy in continental regions are frequently interpreted with respect to past tectonic processes, preserved in the lithosphere as “fossil” fabrics. Models of the present‐day sublithospheric flow (often using absolute plate motion as a proxy) are also used to explain the observations. Discriminating between these different sources of seismic anisotropy is particularly challenging beneath shields, whose thick (≥200 km) lithospheric roots may record a protracted history of deformation and strongly influence underlying mantle flow. Eastern Canada, where the geological record spans ∼3 Ga of Earth history, is an ideal region to address this issue. We use shear wave splitting measurements of core phases such as SKS to define upper mantle anisotropy using the orientation of the fast‐polarization direction ϕ and delay time δt between fast and slow shear wave arrivals. Comparison with structural trends in surface geology and aeromagnetic data helps to determine the contribution of fossil lithospheric fabrics to the anisotropy. We also assess the influence of sublithospheric mantle flow via flow directions derived from global geodynamic models. Fast‐polarization orientations are generally ENE‐WSW to ESE‐WNW across the region, but significant lateral variability in splitting parameters on a ≤100 km scale implies a lithospheric contribution to the results. Correlations with structural geologic and magnetic trends are not ubiquitous, however, nor are correlations with geodynamically predicted mantle flow directions. We therefore consider that the splitting parameters likely record a combination of the present‐day mantle flow and older lithospheric fabrics. Consideration of both sources of anisotropy is critical in shield regions when interpreting splitting observations.
前寒武纪板块构造：来自加拿大哈德逊湾北部的地震证据
影响因子：
5.8
作者：
Bastow I
通讯作者：
Bastow I