Mantle Plumes and Other Mail from the Mantle

Abstract

Study of mantle plumes involves a myriad of disciplines ranging from geochemistry to seismic tomography to mineral physics to fluid dynamics modeling. Evidence from these fields is converging on the notion, put forth in 1980 by Hofmann and White, that plumes originate at the core/mantle boundary layer, fed by thermal activation of ancient subducted slab components. The Sr, Nd and Pb isotope tracer taxonomy of Zindler and Hart delineates four mantle 'species' the uppermost depleted mantle which feeds spreading ridges (DMM), and three others which are transported to the surface at volcanic oceanic islands by upwelling mantle plumes (EM1, EM2 and HIMU). The distinct isotopic evolution of these four species has required 1-2 billion years, and each of the three 'plume' species shows up in pure form in at least two separate geographic regions (in other words, these species are not 'examples of one'; Hofmann, 1992). Figure 1 shows a global isotopic data set consisting of over 1000 analyses of MORB and OIB, with the four mantle species approximately located. Following Carlson (1994), the data are distinguished by hemisphere; the MORB and OIB from the southern hemisphere are far more variable than those from the northern hemisphere. The prevalence of enriched species (EM 1 and EM2) in the southern hemisphere originally led to the delineation of the DUPAL ANOMALY belt