Distribution of Crustal Melt Bodies at the Hot Spot‐Influenced Section of the Galápagos Spreading Centre From Seismic Reflection Images.

Accretion of the lower crust at mid‐ocean ridges is a debated topic, with modern seismic observations pointing to a complex magmatic system that includes an axial multisill system of middle‐ and lower‐crustal melt lenses and near‐ and off‐axis melt bodies. Here we revisit the hot spot‐influenced section of the western Galápagos Spreading Centre and reprocess multichannel seismic reflection data using a wide‐angle seismic tomography model. Our new images show that the magma reservoir in the lower crust at this ridge section is intruded with partially molten melt lenses. The images also show evidence for off‐axis melt lenses, magmatic‐hydrothermal interactions and Moho reflections in this region. We conclude that the similarities between the axial crustal structure of this hot spot‐influenced mid‐ocean ridge and the multisill magmatic structure imaged at the East Pacific Rise indicate that these features are common along the global mid‐ocean ridge system where seafloor spreading is dominated by magmatic accretion. Plain Language Summary: New oceanic crust forms along mid‐ocean ridges from melt extracted from the upwelling mantle. Accretion of the upper crust is well understood, but the process involved in the accretion of the lower crust is still debated. Here we present new seismic images of the crustal magmatic system of the western Galápagos Spreading Centre in the region where the influence of the Galápagos hot spot is largest and ridge magmatism is most robust. Our images show a complex magmatic system that includes lenses of partially molten rock beneath the spreading axis from the midcrust at 1.5 km and throughout the lower crust down to at least 5.4 km below the seafloor and off‐axis melt bodies. Segmentation of the axial magmatic system correlates with presence of hydrothermal features on the seafloor. This system has characteristics very similar to those recently imaged at the East Pacific Rise, indicating that these features are representative of crustal accretion at mid‐ocean ridges where seafloor spreading is dominated by magmatic processes. Key Points: Seismic images from the hot spot‐influenced section of the Galápagos spreading center reveal a multisill magmatic system in the lower crustSpatial correlation between a gap in the axial melt lens and the location of a mature, waning seafloor hydrothermal field suggests magmatic‐hydrothermal interactionsEvidence for off‐axis melt lenses emplaced at the edges of the axial low velocity zone, and weak Moho reflections on the across ridge axis seismic profile, which disappear in the axial zone [ABSTRACT FROM AUTHOR]