Mystery magma channel unveils 20 million years of Galápagos origins

Unlike conventional mantle melts that ascend buoyantly to the surface, forming underwater volcanoes and chains of islands, Naif's imaging revealed a section of partially molten rock known as 'low-degree partial melts.' Surprisingly, these partial melts were sandwiched at the base of the Cocos Plate, approximately 37 miles below the ocean floor.

The significance of this discovery lies in its explanation for the gradual sliding of tectonic plates facilitated by partial melting acting as a lubricant. 

"[The study] also raised several questions about why magma is stored in a thin channel — and where the magma originated from," said Naif in a press release.

Expanding upon his initial breakthrough, Naif embarked on an extensive, years-long investigation, assembling evidence from diverse sources such as geophysical data and geochemical analysis. 

They also carried out direct seafloor sampling with seismic reflection data— a technique used to image layers of sediments and rocks below the surface. "It helps us to see the geology where we cannot see it with our own eyes," Naif explained. 

A 'surprising' link to the Galápagos Islands

 Initially, the researchers noted a considerable presence of widespread intraplate magmatism. Naif explained this as "Volcanism where it is not expected, [that is] basically away from plate boundaries: subduction zones and mid-ocean ridges." 

This phenomenon occurs when a column of hot mantle plume rises deep within the Earth. As it makes it's way up, the plume melts, creating a volcanic chain. A well-known example is the Hawaiian Islands, situated in the middle of the Pacific Ocean.

The new study also revealed that the magma channel, spanning over 100,000 square kilometers, has existed for over 20 million years. “More surprising is that the erupted magma has a chemical fingerprint that links its source to the Galápagos mantle plume," said Naif.

By confirming the presence of past volcanic activity in the region and shedding light on the ongoing storage of magma, the study raises captivating questions about the mechanisms that enable magma to persist in the mantle before sporadically erupting near the seafloor.

The full study was published in Science Advances and can be found here.

Study abstract:

In the past decade, marine geophysical observations have led to the discovery of thin channels at the base of oceanic plates with anomalous physical properties that indicate the presence of low-degree partial melts. However, mantle melts are buoyant and should migrate toward the surface. We show abundant observations of widespread intraplate magmatism on the Cocos Plate where a thin partial melt channel was imaged at the lithosphere-asthenosphere boundary. We combine existing geophysical, geochemical, and seafloor drilling results with seismic reflection data and radiometric dating of drill cores to constrain the origin, distribution, and timing of this magmatism. Our synthesis indicates that the sublithospheric channel is a regionally extensive (>100,000 km2) and long-lived feature that originated from the Galápagos Plume more than 20 Ma ago, supplying melt for multiple magmatic events and persisting today. Plume-fed melt channels may be widespread and long-lived sources for intraplate magmatism and mantle metasomatism.