A multi-sill magma plumbing system beneath the axis of the East Pacific Rise

摘要

Upper oceanic crust at fast-to intermediate-spreading mid-ocean ridges is thought to form from the intrusion and eruption of magma accumulated within a mid-crustal reservoir present beneath the ridge axis~(1-3). However, the mechanisms for formation of the lower crust are debated~(4-8). Observations from pieces of ancient oceanic crust exposed on land - ophiolites - imply that multiple small magma lenses exist throughout the lower crust at mid-ocean ridges and help form the crust~(4,6,7), yet seismic data have imaged only a single lens beneath the innermost axial zones of various mid-ocean ridges1-3. Here we use high-fidelity seismic data to image the crust beneath the East Pacific Rise. We identify a series of reflections below the axial magma lens that we interpret as magma lenses in the upper part of the lower crust. These reflections are present between 9o 200 and 9o 570 N and are located up to 1.5 km below the axial magma lens. From the geometry and amplitude of the reflections in a zone beneath a recent volcanic eruption9, we infer that magma drained from a lower lens helped replenish the axial magma lens above and, perhaps, contributed to the eruption. Our data indicate that a multi-level complex of magma lenses is present beneath the East Pacific Rise and probably contributes to the formation of both the upper and lower crust.