Mantle flow and multistage melting beneath the Galápagos hotspot revealed by seismic imaging

Abstract

Some of Earth's largest magmatic provinces result from the interaction between mid-ocean ridges and near-ridge hotspots, which are hypothesized to overlie plumes of upwelling mantle. Geodynamic models predict that upwelling plumes are sheared by the motion of the overlying tectonic plates and can connect to a nearby mid-ocean ridge by shallow flow beneath thin, young lithosphere. Here we present seismic tomographic images of the upper 300 km of the mantle beneath the Galápagos Archipelago in the eastern Pacific Ocean. We observe a low-velocity anomaly, indicative of an upwelling plume, that is not deflected in the direction of plate motion. Instead, the anomaly tilts towards the mid-ocean ridge at depths well below the lithosphere. These characteristics of the plume-ridge connection beneath the Galápagos Archipelago are consistent with the presence of multiple stages of partial melting, melt extraction, and melt remixing within the plume and surrounding mantle. These processes affect the viscosity of the asthenosphere, alter the upwelling plume and influence the compositions of surface lavas. Our results imply that the coupling between the oceanic plate and plume upwelling beneath the Galápagos is weak. Multistage melting may similarly affect the geophysical and geochemical characteristics of other hotspots.

Triggering of the largest Deccan eruptions by the Chicxulub impact

“…By contrast, a practical estimate for the required length scale for magma extraction can be obtained by calculating the mantle source volume required to produce the ~500,000 km 3 volume of the Wai Subgroup lava fl ows. Assuming an average 2%-3% partial melt content (e.g., Villagomez et al, 2014) in the plume head (Fig. 3), we obtain a length scale of order L = 300-500 km, comparable to the size of the plume head itself.…”

A 1.5 Ma record of plume-ridge interaction at the Western Galápagos Spreading Center (91°40′–92°00′W)

“…Seismic tomography of the upper mantle beneath the Galápagos Archipelago shows that the low-velocity anomaly associated with the Galápagos plume rises into the upper mantle beneath the westernmost islands but bends to the north at a depth of ~100 km between ~90-92°W (Villagómez et al, 2014). Although the presently available tomography doesn't resolve the anomaly north of 1°N latitude, it is likely that the northern part of the plume extends to the WGSC located at ~2°N.…”

“…Recent seismic tomographic studies of the upper mantle, extending to depths of up to 400 km beneath the Galápagos archipelago, reveal flow of plume material towards the GSC (Villagómez et al, 2014 and references therein). The observed low-velocity seismic anomaly beneath the archipelago can be interpreted to represent an upwelling mantle plume located between ~90.5 to 91.5°W that bends northwards at depths below the hydrous peridotite solidus (>100 km).…”

Hotspots and Mantle Plumes

“…5.4), probably due to the lower resolution of the tomographic model there (Zhao 2007). Villagomez et al (2014) presented a local tomography of the upper 300 km of the mantle beneath the Galapagos Archipelago. They revealed a low-V anomaly, indicative of an upwelling plume, which tilts towards the mid-ocean ridge at depths well below the lithosphere.…”