Plumes of hot, buoyant material are thought to rise from the deepest mantle, near the core-mantle boundary.
In the shallow mantle, the plumes partially melt, and the melt is erupted at the surface at hotspot volcanoes. Several hotspot volcanoes, including those in Hawaii, Samoa, and the Marquesas, exhibit two parallel volcanic lineaments that are geochemically distinct. This geochemical separation is thought to result from the plumes being sourced from the northern side of a large, enriched geochemical and seismological anomaly in the deepest mantle.
The south side of each plume then entrains the geochemically enriched material, which is reflected in the geochemical zonation of hotspot volcanoes at the surface. To test this hypothesis, Jarod Payne and colleagues examine volcanic lineaments in the Society Islands hotspot, which is located to the south of a seismologically anomalous region in the deep mantle.
They find that the northern volcanic trend in the Society Islands is enriched relative to the southern volcanic trend. This observation is consistent with plume zonation arising from an enriched geochemical anomaly in the deepest mantle, and the relative geometry of the plume and the geochemical anomaly governs the sense of zonation in Pacific hotspots.
Jarod A. Payne et al. (Matthew G. Jackson, corresponding), Dept. of Earth Sciences, Boston University, 675 Commonwealth Avenue, Boston, Massachusetts 02215, USA. Posted online 19 October 2012; doi: 10.1130/G33273.1