Differential subsidence of the forearc wedge of the Ryukyu (Nansei-Shoto) Arc caused by subduction of ridges on the Philippine Sea Plate
Differential subsidence of the forearc wedge of the Ryukyu (Nansei-Shoto) Arc caused by subduction of ridges on the Philippine Sea Plate
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DOI：
10.1016/j.tecto.2017.08.025
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发表时间：
2017-10
期刊：
影响因子：
2.9
通讯作者：
Y. Okamura;A. Nishizawa;M. Oikawa;D. Horiuchi
中科院分区：
文献类型：
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作者：
Y. Okamura;A. Nishizawa;M. Oikawa;D. Horiuchi
中中新世以来，菲律宾海板块携带多个洋脊俯冲到琉球岛弧之下。由于没有广泛的增生棱柱一直在增长沿着琉球海沟，弧提供了一个机会，研究脊俯冲对弧前楔结构的影响，并提供了一个线索，以重建古老的板块运动的PSP，推断已改变了西北和NNW之间。为了检验这一观点，我们澄清了结构的琉球弧前楔的地震剖面和测深数据的基础上，并将它们与山脊俯冲。琉球岛弧普遍存在前新近纪和新近纪岩石之间的侵蚀不整合，根据侵蚀不整合深度的差异，将弧前楔体从西南向东北划分为Ⅰ ~ Ⅳ带。我们将这四个带与沿着琉球海沟向东北或西南方向移动的洋脊俯冲位置进行了对比。带I的下方是大量下沉的不整合面，我们将其结构归因于PSP西缘（包括吕宋弧）俯冲导致的欧亚板块撕裂。II区由浅层侵蚀不整合上的宽阔阶地组成，目前还没有已知的山脊在该区俯冲。III带以向海下降的不整合面为特征，覆盖着一套厚的新近纪沉积物，与NW-SE向的大东海脊和E-W向的奄美高原的俯冲有关。IV带具有较深的不整合面和斜坡几何形状，对应于NNW-SSE走向九州-帕劳海岭的俯冲。琉球前弧的构造与PSP上的脊的俯冲一致，这表明PSP的板块运动的变化可以通过进一步的详细测量精确地重建。
The Philippine Sea Plate (PSP) carrying several ridges has been sudbucting under the Ryukyu (Nansei-Shoto) Arc since middle Miocene. Because no extensive accretionary prism has been growing along the Ryukyu Trench, the arc provides an opportunity to examine effects of ridge subduction on structure of the forearc wedge and a clue to reconstruct ancient plate motion of the PSP that is inferred to have changed between NW and NNW. To examine this perspective, we clarified structure of the Ryukyu forearc wedge based on seismic profiles and bathymetric data and related them to ridge subduction. An erosional unconformity between pre-Neogen and Neogene rocks is widely recognized through the Ryukyu Arc, and we divided the forearc wedges into Zones I to IV from southwest to northeast by difference of depth of the erosional unconformity. We correlated these four zones to the locations of ridge subduction that have been shifting NE or SW along the Ryukyu Trench. Zone I is underlain by the largely subsided unconformity and we attributed the structure to tearing of the Eurasia plate due to subduction of the western margin of the PSP including the Luzon Arc. Zone II consists of a wide terrace on the shallow erosional unconformity, and no ridge that was subducting in this zone is known. Zone III is characterized by the seaward descending unconformity covered with a thick sequence of Neogene sediments and is related to subduction of the NW-SE trending Daito Ridge and theE-W trending Amami Plateau. Zone IV has the deeper unconformity and slope geometry and corresponds to subduction of the NNW-SSE trending Kyushu-Palau Ridge. The structure of the Ryukyu forearc is consistently related to subduction of ridges on the PSP, suggesting that the change of the plate motion of the PSP can be precisely reconstructed by further detailed survey.