Additional subsidence of oceanic basins compared to the half-space cooling prediction is thought to be a dynamic response to the underlying mantle convection induced by slab sinking. Here, we identified a significantly elevated proportion (10%–20%) of recycled oceanic crust (ROC) in the source of mid-ocean-ridge basalts (MORBs) from the South China Sea (SCS), illustrating the ROC accumulation within a confined upper-mantle range, possibly as a result of the long-term surrounding subduction events. The presence of this lithological heterogeneity in the ROC leads to an increase in mantle density by 0.45%–0.90% at most, thereby contributing to the observed excessive subsidence in the SCS basin when compared to other small basins affected by dynamic topography, while open oceans experience subsidence primarily due to thermal cooling. We propose that the ROC-induced density change in the upper mantle is crucial for generating the topographic anomalies in oceanic basins influenced by subducted slabs, alongside dynamic topography caused by mantle flow.

中文翻译：

---

地幔源区洋壳循环导致大洋盆地过度沉降：东南亚海洋地形的新视角


与半空间冷却预测相比，大洋盆地的额外沉降被认为是对板片下沉引起的底层地幔对流的动态响应。在这里，我们发现南海（SCS）洋中脊玄武岩（MORB）来源中再生洋壳（ROC）的比例显着升高（10%–20%），说明了ROC在一个区域内的积累。有限的上地幔范围，可能是周围长期俯冲事件的结果。 ROC中这种岩性不均匀性的存在导致地幔密度最多增加0.45%–0.90%，从而导致与其他受动态地形影响的小盆地相比，南海盆地发生了过度沉降，而公海主要由于热冷却而发生沉降。我们认为，ROC 引起的上地幔密度变化对于在受俯冲板片影响的大洋盆地中产生地形异常以及地幔流引起的动态地形至关重要。