Carnegie Fellow Nick Schmerr and colleagues recently published a paper, entitled “Deep mantle plumes and convective upwelling beneath the Pacific Ocean,” in Earth and Planetary Science Letters (EPSL). The mineral olivine is known to undergo solid-solid phase transitions at approximately 410 and 660 km depth beneath the Earth’s surface, though the precise depth of the phase transitions depends on the local temperature and composition of the mantle. The group used underside shear-wave reflections to map phase transition depths beneath the Pacific Ocean and implied lateral changes in mantle temperature and chemistry.

The study reveals evidence for a hotter mantle beneath Hawaii and in a large region of the southern Pacific that is associated with a number of hotspot island chains, deep mantle upwelling, and the paleo-eruption location of the Ontong Java Plateau large igneous province. Schmerr and colleagues also detected the presence of cold, subducted lithosphere beneath the New Zealand, Tonga-Fiji, and New Hebrides subduction zones. Their results support the hypothesis that the mantle convects as a whole, with upwellings located at the edges of the large low-shear-velocity province at the base of the mantle. For more information, see the EPSL paper.