Ocean volcanoes may be the echoes of ancient continental breakups, according to a new study. The research suggests that long after continents rift apart, instabilities in the mantle created by the breakups continue to shape the Earth's surface. This phenomenon could explain the existence of ocean volcanoes and the formation of underwater mountain ranges like the Christmas Island Seamount in the Indian Ocean. The study's lead author, Thomas Gernon, calls this a "completely new mechanism" that also influences the composition of the mantle. The unusual magma found in these volcanoes contains minerals that resemble continental crust rather than oceanic crust, leading researchers to hypothesize that these volcanoes are dredging up remnants of oceanic crust that was subducted into the mantle long ago, along with coastal sediments from the continents. Another theory is that mantle plumes, or upwellings of rock from the deep mantle, are bringing ancient continental material back to the surface. However, Gernon and his colleagues suggest that these volcanoes may be fed by a variety of continental rocks that peel off into the mantle after cataclysmic continental breakups. They examined volcanic rocks from the Walvis Ridge, an ocean ridge off the coast of Africa, and found a pattern where older eruptions contained more continent-like magma, gradually transitioning to more ocean-rock-like compositions. Computer models revealed that after a continental breakup, waves in the mantle can scrape continental crust off the bottom, enriching the mantle with mineral-enriched material. This process takes millions of years to complete and supplies the mantle with tens of millions of years' worth of continental rock, peaking about 50 million years after the rift. The study's findings highlight the long-lasting impacts of continental breakups, with the mantle still feeling the effects long after the continents have separated. This discovery opens up new avenues for understanding the complex dynamics of the Earth's mantle and the formation of ocean volcanoes.
