The oceanic lithosphere is a primary component of the plate tectonic system, yet its evolution and its asthenospheric interaction have rarely been quantified by in situ imaging at slow spreading systems. We use Rayleigh wave tomography from noise and teleseismic surface waves to image the shear wave velocity structure of the oceanic lithosphere‐asthenosphere system from 0 to 80 My at the equatorial Mid‐Atlantic Ridge using data from the Passive Imaging of the Lithosphere‐Asthenosphere Boundary (PI‐LAB) experiment. We observe fast lithosphere (V_SV > 4.4 km/s) that thickens from 20–30 km near the ridge axis to ~70 km at seafloor >60 My. We observe several punctuated slow velocity anomalies (V_SV < 4.1 km/s) in the asthenosphere between 50 and 150 km depth, not necessarily focused beneath the ridge axis. Some of the slow velocity regions are located within 100 km of the ridge axis, but other slow velocity regions are observed at distances > 400 km from the ridge. We observe a high velocity lithospheric downwelling drip beneath 30 My seafloor that extends to 80–130 km depth. The asthenospheric slow velocities likely require partial melt. Although melt is present off axis, the lack of off‐axis volcanism suggests the lithosphere acts as a permeability boundary for deeper melts. The punctuated and off‐axis character of the asthenospheric anomalies and lithospheric drip suggests small‐scale convection is active at a range of seafloor ages. Small‐scale convection and/or more complex mantle flow may be aided by the presence of large offset fracture zones and/or the presence of melt and its associated low‐viscosities and enhanced buoyancies.

中文翻译：

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从瑞利波层析成像看赤道大西洋海洋岩石圈的演变，从PI-LAB实验获得小规模对流的证据

海洋岩石圈是板块构造系统的主要组成部分，但很少通过慢速扩散系统的原位成像来量化其演化和软流圈相互作用。我们使用来自噪声和远震地表波的瑞利波层析成像技术，利用来自岩石圈-软流层边界的被动成像（数据），在赤道中大西洋海脊从0到80 My的海洋岩石圈-软流层系统的横波速度结构成像。 PI‐LAB）实验。我们观察到快速岩石圈（V _SV  > 4.4 km / s）从脊轴附近的20–30 km增厚到海底> 60 My处的〜70 km。我们观察到一些标点化的慢速异常（V _SV 小于50公里和150公里深度之间的软流圈中的<4.1 km / s），不一定聚焦在山脊轴线下方。一些慢速区域位于距山脊轴100 km以内，但其他慢速区域则在距山脊> 400 km处观察到。我们观察到在30 My海底以下的岩石圈高速下行滴落，延伸至80-130 km深度。软流圈的慢速可能需要部分融化。尽管熔融物存在于轴外，但缺乏轴外火山作用表明岩石圈可作为深层熔融物的渗透边界。软流圈异常和岩石圈滴漏的点状和偏轴特征表明，小尺度对流在一定海底年龄范围内是活跃的。