Subducting seamounts and deformation of overriding forearc wedges around Japan
Subducting seamounts and deformation of overriding forearc wedges around Japan
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日本周围的海山俯冲和上覆前弧楔的变形
DOI：
10.1016/0040-1951(89)90392-2
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发表时间：
1989
期刊：
影响因子：
2.9
通讯作者：
Y. Okamura
中科院分区：
文献类型：
--
作者：
T. Yamazaki;Y. Okamura
根据磁异常、形态和地质结构，在日本周围确定了两座内海沟斜坡下的俯冲海山。第一个位于日本海沟和千岛海沟交界处的内海沟斜坡脚下。另一个发生在土佐贝稍微向海的斜坡之下（四国外海南海海槽沿着海沟斜坡坡折处的基底高处）。海山成因的磁异常伴随着弧前楔的特征形态，向陆地的涌浪和向海的低压。内海沟斜坡下的海山保留了磁化作用，显示出相当一致的方向，这表明俯冲海山大致保持了原来的形状。弧前楔的形态可以解释为洋壳上的俯冲海山向前和向上推动弧前物质。俯冲海山对弧前楔体的变形延伸到弧前盆地。海山比内斜坡材料更坚固，变形性更小，并且不会被刮到内海沟斜坡上。介绍了日本周围变形内海沟斜坡的另外两个例子，可以用地形高点的俯冲来解释。一个例子是九州-帕劳海脊和南海海槽交界处东北部内海沟斜坡脚下的一个凹陷。另一个是围绕Daiichi-Kashima海山沿着日本海沟的海沟内斜坡的复杂形态区域。
Two subducting seamounts under inner trench slopes have been identified around Japan on the basis of magnetic anomalies, morphology and geological structure. The first one is located under the foot of the inner trench slope at the junction between the Japan Trench and the Kuril Trench. Another one occurs beneath the slope slightly seaward of the Tosabae (the basement high at the trench slope break along the Nankai Trough off Shikoku). The magnetic anomalies of seamount origin are accompanied by the characteristic morphology of a forearc wedge i.e., a swell landward and a depression seaward. The seamounts beneath the inner trench slopes have preserved magnetization showing reasonably consistent directions, which suggests that the subducting seamounts have kept roughly their original shapes. The morphology of the forearc wedge can be explained by a subducting seamount on the oceanic crust pushing the forearc material forward and upward. Deformation of the forearc wedge by the subducting seamount extends to the forearc basin. The seamounts are stronger and less deformable than the inner slope material and are not offscraped onto inner trench slopes.Two other examples of deformed inner trench slopes around Japan which can be explained by subduction of topographic highs are presented. One example is a depression on the foot of the inner trench slope northeast of the junction between the Kyushu-Palau Ridge and the Nankai Trough. Another one is an area of complex morphology of the inner trench slope along the Japan Trench around the Daiichi-Kashima Seamount.