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

Abstract

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Geoscience 7 (2014): 825-829, doi:10.1038/ngeo2272.The mid-crust axial magma lens detected at fast and intermediate spreading mid-ocean ridges is believed to be the primary magma reservoir for formation of upper oceanic crust. However, the mechanism behind formation of the lower crust is a subject of ongoing debate. The sheeted sill model proposed from observations of ophiloites requires the presence of multiple lenses/sills throughout lower crust but only a single lens is imaged directly beneath the innermost axial zone in prior seismic studies . Here, high-fidelity seismic data from the East Pacific Rise reveal series of reflections below the axial magma lens that we interpret as mid-lower crustal lenses. These deeper lenses are present between 9°20-57′N at variable two-way-travel-times, up to 4.6 s (~1.5 km beneath the axial magma lens), providing direct support for the sheeted sill model. From local changes in the amplitude and geometry of the events beneath a zone of recent volcanic eruption, we infer that melt drained from a lower lens contributed to the replenishment of the axial magma lens above and, perhaps, the eruption. The new data indicate that a multi-level sill complex is present beneath the East Pacific Rise that likely contributes to the formation of both the upper and lower crust.This research was supported by NSF awards OCE0327872 to J. C. M., S. M. C., OCE- 0327885 to J. P. C., and OCE0624401 to M. R. N.2015-04-1