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Sulfur Isotopic Evidence on the Age of Recycled Surface Material in the Tristan-Gough Plume Source

The recycling hypothesis argues that mantle plumes contain recycled surface material of oceanic crust / sediments. To further our understanding of the geodynamic evolution of Earth’s interior constraints are required on the time spent by such recycled material before it re-surfaces in mantle plume volcanism. Most geochemical tools fail because compositional variability masks age information. A new promising tool are multiple-sulfur isotopes. At present-day, processes modifying sulfur produce isotopic fractionations that depend on the relative mass differences between its different isotopes. In contrast, Archean/earliest Proterozoic sediments exhibit mass-independently fractionated sulfur isotopes (MIF-S) acquired through photochemical reactions in the oxygen-poor atmosphere. The persistence of recycled MIF-S through subduction and eventual rise in a mantle plume has been demonstrated for two South Pacific plumes [1,2]. Is such old surface material a common or rare component in plume sources? Here we present sulfur isotopes of mineral-hosted sulfide inclusions from rocks related to the major 130 Ma-long-lived Tristan-Gough plume system with a root at the core-mantle boundary related to the African LLSVP. Preliminary data on 12 sulfide inclusions from 3 samples show negative d 34 S values from -6 ± 0.6 to slightly positive values of 0.7 ± 0.4 ‰ (2 s error) and D 33 S of -0.18 to 0.17 ( ± 0.12). These data fall in the range of overlapping values between Archean and Proterozoic sediments and do not allow an unequivolcal assignment