Geochem. Geophys. Geosys. http://doi.org/p28 (2013)

Ocean islands, such as Hawaii, are typically created by voluminous volcanic activity caused by thermal or compositional anomalies in the underlying mantle. Seismic analyses of oceanic lithosphere in the Atlantic and Southwest Indian oceans, however, reveal chains of ancient ocean islands generated by tectonic processes, rather than volcanism.

Camilla Palmiotto at the University of Bologna, Italy, and colleagues used seismic reflection data to image the structure of the crust in the equatorial Atlantic Ocean and the southwest Indian Ocean. In both locations, the images reveal ridges of oceanic rocks that had been extensively eroded flat before caps of carbonate rocks were deposited on top. Although now located about 500 to 1,000 metres beneath the ocean surface, the erosion must have taken place at sea level by the action of waves, implying that the ridges once formed chains of ocean islands. Strontium-isotopic dating of the carbonate rocks, which formed on top of the islands after they sunk back below sea level, show that the ridges must have been above sea level between 12 to 2 million years ago.

The ridges are bounded by large faults, so the researchers suggest that the islands were uplifted by tectonic movements, rather than anomalous volcanic activity.