The Ayu Trough, located in the equatorial western Pacific, is the only divergent boundary surrounding the Philippine Sea Plate. A mid-ocean ridge spreading in the N-S direction near low-latitude regions presents low geomagnetic anomalies, thereby complicating the constraining of the trough’s spreading rate based on the geomagnetic signal from the magnetized seafloor. According to previous studies, the Ayu Trough has been open since ∼25 Ma, with a half-spreading rate of 4.1–8.1 mm/yr. This implies that the trough belongs to the ultraslow-spreading mid-ocean ridge category with a full-spreading rate below 20 mm/yr. However, the geochemical signatures of the rock samples from the Ayu Trough do not exhibit the unique characteristics of ultraslow-spreading ridges, including the enriched mid-ocean ridge basalts (E-MORB) with high rare earth element (REE) concentrations and abundant light rare earth elements (LREE). Rather, the sampled rocks from the entire trough-axis exhibit the typical features of the normal mid-ocean ridge basalts (N-MORB) with low REE concentrations. The contradictory inferences made from geochemical results suggest that the Ayu Trough did not undergo an ultraslow-spreading but rather a considerably rapid spreading over a short period compared to the estimates made by previous studies. The modified interpretation for the spreading rate of the Ayu Trough can be associated with the global plate reconstruction model, considering the major plate reorganization in East Asia. Around 15 Ma, a series of significant tectonic events occurred in East Asia and the western Pacific. The global models for East Asia imply that the spreading of the Ayu Trough could have been initiated afterwards. Based on our geochemical analysis of the MORB on the Ayu Trough and the global plate model, we argue that the spreading of the Ayu Trough was initiated after ∼15 Ma during the major plate reorganization in East Asia, and not in ∼25 Ma as reported by previous studies. Therefore, the spreading occurred only for a period of about 10 Myr at a relatively rapid full-spreading rate of >20 mm/yr. The massive sediments with a thickness of approximately 50–70 m on the spreading-axis of the Ayu Trough reinforce the estimated cessation time of the trough. In addition, the V-shaped seafloor of the Ayu Trough and the unclear transform fault may be interpreted as topography formed by a propagation of rift or mantle melting. Therefore, the trough does not have to be simultaneously opened throughout the axis, and its spreading rate could be higher than previously estimated.

阿尤海槽位于赤道西太平洋，是菲律宾海板块周围唯一的分界线。低纬度地区附近沿南北向扩展的洋中脊呈现低地磁异常，从而使基于磁化海底的地磁信号对海槽扩展速率的约束变得复杂。根据之前的研究，香鱼海槽自~25Ma以来就已开放，半扩张率为4.1-8.1毫米/年。这意味着该海槽属于超慢速扩张的洋中脊类别，其完全扩张速度低于 20 毫米/年。然而，香鱼海槽岩石样本的地球化学特征并未表现出超慢速扩张脊的独特特征，包括富含稀土元素（REE）和丰富的轻稀土元素（LREE）的富集洋中脊玄武岩（E-MORB）。相反，从整个槽轴取样的岩石表现出稀土浓度较低的正常洋中脊玄武岩（N-MORB）的典型特征。根据地球化学结果得出的矛盾推论表明，与之前研究的估计相比，香鱼海槽并未经历超慢速扩张，而是在短时间内经历了相当快的扩张。考虑到东亚板块的主要重组，对香鱼海槽扩张速率的修正解释可以与全球板块重建模型联系起来。15Ma左右，东亚和西太平洋地区发生了一系列重大构造事件。东亚的全球模型表明香鱼海槽的扩张可能是在之后开始的。根据我们对香鱼海槽 MORB 和全球板块模型的地球化学分析，我们认为香鱼海槽的扩张是在东亚主要板块重组期间约 15 Ma 之后开始的，而不是报道中的约 25 Ma通过之前的研究。因此，传播仅发生了约 10 Myr 的时间，且完全传播速率相对较快，大于 20 毫米/年。香鱼槽扩展轴上厚度约为 50-70 m 的大量沉积物强化了香鱼槽停止时间的估计。此外，阿玉海槽的V形海底和不明确的转换断层可能被解释为裂谷或地幔熔融扩展形成的地形。所以，