Surface friction of subducting seamounts influences deformation of the accretionary wedge
Surface friction of subducting seamounts influences deformation of the accretionary wedge
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DOI：
10.1016/j.tecto.2022.229644
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发表时间：
2022-11
期刊：
影响因子：
2.9
通讯作者：
Yuichi Okuma;A. Noda;H. Koge;Yasuhiro Yamada;A. Yamaguchi;J. Ashi
中科院分区：
文献类型：
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作者：
Yuichi Okuma;A. Noda;H. Koge;Yasuhiro Yamada;A. Yamaguchi;J. Ashi
俯冲洋板块上的起伏地形引起增生楔的显著变形。特别是，海山的俯冲被认为会导致：1）向陆凹陷地形的发展，如凹进和锯齿状地貌; 2）增生楔内的压缩; 3）与多个断层形成有关的隆起对原始逆冲岩席结构的扰动。然而，根据以前的地震剖面，一些俯冲海山提供了微弱楔形变形的暗示性证据，而不是以前模型实验中显示的强烈压缩和隆起。由于已知增生楔的横截面形状受到楔的内部摩擦和基底摩擦的强烈约束，本研究使用两个海山模型的模拟实验，分别具有低摩擦和高摩擦，来评估俯冲海山的摩擦条件对上板块变形的影响。结果表明，高摩擦海山的俯冲作用导致增生楔的持续挤压和抬升，板块边界断裂带由不连续的多条断层组成，断层垂直错动，部分重叠，形成厚的变形带。相比之下，低摩擦海山与一个相对较薄的楔形体和一个单一的板块边界断层有关，与高摩擦海山相比，这导致较少的压缩。在低摩擦海山俯冲过程中，随着海山上沉积物厚度的减小，增生楔局部增大，这在以往的研究中是没有报道过的。在希库朗吉边缘的俯冲班尼特诺尔海山周围的楔形变形模式可以解释低摩擦海山俯冲中观察到的机制。从这些结果中，我们得出结论，在海山俯冲的早期阶段，在海山表面的摩擦条件是一个主导的楔变形过程中的控制。
Undulating topography on a subducting oceanic plate causes substantial deformation of the accretionary wedge. In particular, the subduction of a seamount is considered to induce 1) the development of landward concave topography such as reentrant and indented features, 2) compression within the accretionary wedge, and 3) disturbance of the primary thrust-sheet structures by uplift associated with the formation of multiple faults. However, according to previous seismic profiles, some subducting seamounts have provided suggestive evidence for weak wedge deformation rather than strong compression and uplift that were indicated in the previous model experiments. As the cross-sectional shape of an accretionary wedge is known to be strongly constrained by the internal and basal friction of the wedge, this study evaluates the effect of the frictional conditions of a subducting seamount on the deformation of the upper plate using analog experiments of two seamount models with low and high friction, respectively. Results show that subduction of a high-friction seamount causes continuous compression and uplift of the accretionary wedge, with the plate boundary fault zone composed of discontinuous multiple faults that offset vertically and partially overlapped to form a thick deformation zone. In contrast, a low-friction seamount is associated with a relatively thin wedge and a single plate boundary fault, which results in less compression compared with a high-friction seamount. During the subduction of a low-friction seamount, the accretionary wedge grows locally as the thickness of sediment on the seamount decreases, which has not been reported in previous studies. The wedge deformation pattern around the subducting Bennett Knoll Seamount in the Hikurangi Margin could be explained by the mechanism observed in the low-friction seamount subduction. From these results, we conclude that the frictional conditions on the seamount surface are a dominant control on the process of wedge deformation during the early stages of seamount subduction.