20-EPN2-064: High-precision isotope analysis of individual melt inclusions

20-EPN2-064: High-precision isotope analysis of individual melt inclusions – Reassessing the compositional variability of Earth’s mantle

Visit by Felix Genske and Misha Böhnke, Westfälische Wilhelms-Universität Münster, Institut für Mineralogie (Germany) to TA2.1 VU Geology and Geochemistry radiogenic and non-traditional stable Isotope Facility (GGIF).
Dates of visit: 14-19 November 2022

Report Summary: In a unique approach, we acquired high precision Nd isotope data on well-characterised sample sets of silicate melt inclusions (MI) from the islands of Gough and Tristan da Cunha in the South Atlantic ocean. These data were collected using a Thermo Scientific Triton Plus TIMS at the VU Amsterdam. Melt inclusions from single or multiple olivine crystals were analysed and the new data provide insights into the magnitude, origin, and mode of sampling of the isotopically diverse materials that represent Earth’s mantle. The most prominent finding of this study is the extended isotopic variability of mantle melts, indicating that the mantle itself is more heterogeneous than assumed from studies of lavas (i.e. whole rocks). Further, the new data from melt inclusions entrapped in lavas from different islands greatly extend the known isotopic variation not only from individual eruption centres but also on a global scale.

Although observed small-scale mantle heterogeneity may exist down to the meter-, perhaps even cm-scale, the former also implies that distinct isolated large-scale (100’s km) reservoirs in Earth’s mantle (and other rocky planets) may not exist. Instead, the efficiency of mantle mixing via convection with time plays a more important role than previously thought; indeed, the existence of the full spectrum of mantle heterogeneity may be captured within single eruptions. As a consequence, the significance of large-scale distinct mantle domains detected by seismic imaging is questioned by our findings.