Tectonic evolution of the triple junction off central Honshu for the past 1 million years
Tectonic evolution of the triple junction off central Honshu for the past 1 million years
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本州中部附近三重交界点过去100万年的构造演化
DOI：
10.1016/0040-1951(89)90386-7
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发表时间：
1989
期刊：
影响因子：
2.9
通讯作者：
A. Taira
中科院分区：
文献类型：
--
作者：
T. Seno;Y. Ogawa;H. Tokuyama;E. Nishiyama;A. Taira
我们讨论了几种模式的演变沟三重结中部本州在过去的1百万年。根据该地区现有的板块运动学、形态学、重力和地震反射剖面数据，研究区的特点是大型盆地，7-8公里深的内低海沟斜坡上的菲律宾海一侧和深（9公里）伊豆-小笠原海沟以东。在盆地和海沟之间，有6-7公里深的基底高地。由于菲律宾海板块相对于欧亚大陆（日本东北部）以3厘米/年的速度向西北偏西方向运动，与相模海槽的走向近平行，因此三重结合点不稳定。一般来说，我们可以预期菲律宾海和太平洋板块之间的边界区域将扩大，因为太平洋板块不太可能跟随菲律宾海板块的撤退，因为欧亚大陆东南角的阻挡。结区的上述特殊形态可能是由于缺乏稳定性造成的。然而，有几种可能的方法来解释上述形态。我们的重力模型横跨沟基高盆区表明，基底高点是由低密度物质（1.8-2 g/cm 3）。因此，我们拒绝了地幔底辟模型，该模型认为基底高点是由退缩的菲律宾海板块和太平洋板块之间的蛇纹岩底辟注入形成的，拉伸盆地模型认为盆地是由菲律宾海板块楔的拉伸形成的。我们估计最大盆地的延伸约为10公里。我们重建了1 Ma时的形态，通过在盆地闭合后将菲律宾海板块向东移动20 km，从而获得了1 Ma海沟的8 km深度，这与现在的日本海沟相似。虽然这个伸展盆地模型可以解释盆地和深沟的形成，但其他模型也同样可能。例如，排泄模型解释了盆地的起源，菲律宾海基底从下面的基底高的排泄，而增生模型解释了基底高的Izu-Bonin海沟楔沉积物的增生。在这两种模型中，我们都可以重建出1 Ma的海沟深度约为8 km，与伸展盆地模型相似，盆地基底的变形是区分这两种模型的最佳标准。多道地震反射剖面显示，最大盆地的基底被正断层切割，特别是在其东部边缘。这表明拉伸盆地模型最有可能。然而，沉积物的上部表明，东部的基底最近被抬升。这种隆起可能是由于最近（0.5马）开始在这个基底高的沟槽楔沉积物的增生。
We discuss several models of the evolution of the trench-trench-trench triple junction off central Honshu during the past 1 m.y. on the basis of plate kinematics, morphology, gravity and seismic reflection profile data available for the area. The study area is characterized by large basins, 7–8 km deep on the inner lower trench slope on the Philippine Sea side and the deep (9 km) Izu-Bonin Trench to the east. Between the basins and the trench, there are 6–7 km-deep basement highs. The triple junction is unstable due to the movement of the Philippine Sea plate at a velocity of 3 cm/yr in WNW direction with respect to Eurasia (Northeast Japan), subparallel to the strike of the Sagami Trough. Generally we can expect the boundary area between the Philippine Sea and Pacific plates to be extended because the Pacific plate is unlikely to follow the retreating Philippine Sea plate due to the obstruction of the southeastern corner of Eurasia. The above peculiar morphology of the junction area could have resulted from this lack of stability. However, there are several possible ways to explain the above morphology.Our gravity model across the trench-basement high-basin area shows that the basement highs are made of low-density materials (1.8–2 g/cm3). Thus we reject the mantle diapir model which proposes that the basement highs have been formed by diapiric injection of serpentinites between the retreating Philippine Sea plate and the Pacific plate.The stretched basin model proposes that the basins have been formed by stretching of the Philippine Sea plate wedge. We estimated the extension to be about 10 km at the largest basin. We reconstructed the morphology at 1 Ma by moving the Philippine Sea plate 20 km farther to the east after closing the basins, and thus obtained 8 km depth of the 1 Ma trench, which is similar to that of the present Japan Trench to the north. Although this stretched basin model can explain the formation of the basins and the deep trench, other models are equally possible. For instance, the eduction model explains the origin of the basin by the eduction of the Philippine Sea basement from beneath the basement high, while the accretion model explains the basement highs by the accretion of the Izu-Bonin trench wedge sediments. In both of these models we can reconstruct the 1 Ma trench depth as about 8 km, similar to that of the stretched basin model.The deformation of the basement of the basins constitutes the best criterion to differentiate between these models. The multi-channel seismic reflection profiles show that the basement of the largest basin is cut by normal faults, in particular at its eastern edge. This suggests that the stretched basin model is most likely. However, the upper part of the sediments shows that the basement high to the east has been recently uplifted. This uplift is probably due to the recent (0.5 Ma) start of accretion of the trench wedge sediments beneath this basement high.