We present a 2D P-wave velocity model from the outer rise region of the Lesser Antilles island arc, the first wide-angle seismic study of outer rise processes at an Atlantic subduction zone. The survey consists of 46 OBS receivers over a 174 km profile with velocities resolved to 15 km below top basement. The final velocity model, produced through tomographic inversion, shows a clear decrease in the velocity of the lower crust and upper mantle of the incoming plate as it approaches the trench. We attribute this drop to outer rise bend-related hydration, similar to Pacific cases, but superimposed on spatial variations in hydration generated at the slow-spreading ridge axis. In thin, tectonically controlled crust formed under magma-poor spreading conditions the superposition of these sources of hydration results in compressional velocities as low as 6.5 km s⁻¹ beneath the PmP reflector. In contrast, segments of crust interpreted as having formed under magma-rich conditions show velocity reductions and inferred hydrous alteration more like that observed in the Pacific. Hence, variations in the style of crustal accretion, which is observed on 50–100 km length scales both along and across isochrons, is a primary control over the distribution of water within the slab at Atlantic subduction systems. This heterogeneous pattern of water storage within the slab is likely further complicated by along strike variations in outer rise bending, subducting fracture zones and deformation at segment ends and may have important implications for our understanding of long-term patterns of hazard at Atlantic subduction systems.

中文翻译：

---

地壳吸积变化在确定大西洋俯冲带板片水化中的作用

我们提出了一个来自小安的列斯群岛弧外上升区域的二维 P 波速度模型，这是大西洋俯冲带外上升过程的第一次广角地震研究。该调查由 46 个 OBS 接收器组成，覆盖 174 公里的剖面，速度解析为地下室顶部以下 15 公里。通过层析反演得到的最终速度模型显示，当进入的板块接近海沟时，下地壳和上地幔的速度明显下降。我们将这种下降归因于外上升弯曲相关的水合作用，类似于太平洋的情况，但叠加在缓慢扩张的山脊轴产生的水合作用的空间变化上。在薄，^-1在 PmP 反射器下方。相比之下，被解释为在富含岩浆的条件下形成的地壳部分显示出速度降低和推断的含水蚀变，更像是在太平洋观察到的。因此，沿等时线和跨等时线在 50-100 公里长度尺度上观察到的地壳吸积类型的变化是对大西洋俯冲系统板块内水分布的主要控制。由于外部上升弯曲、俯冲断裂带和段端变形的沿走向变化，板片内的这种异质储水模式可能会进一步复杂化，并且可能对我们理解大西洋俯冲系统的长期危险模式具有重要意义。