EGU21-6416, updated on 04 Mar 2021
https://doi.org/10.5194/egusphere-egu21-6416
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Sulfur isotope evidence of geochemical zonation of the Samoan mantle plume

James Dottin1, Jabrane Labidi3, Matthew Jackson4, and James Farquhar1,2
James Dottin et al.
  • 1University of Maryland, College Park, Geology, College Park, United States of America (jdottin@umd.edu)
  • 2Earth System Science Interdisciplinary Center, College Park, MD 201742, United States
  • 3Universite de Paris Institut de physique du globe de Paris, CNRS, F75005 Paris, France
  • 4Department of Earth Science, University of California, Santa Barbara, CA 93106, United States

The radiogenic Pb isotope compositions of basalts from the Samoan hotspot suggest various mantle endmembers contribute compositionally distinct material to lavas erupted at different islands [1]. Basalts from the Samoan islands sample contributions from all of the classical mantle endmembers, including extreme EM II and high 3He/4He components, as well as dilute contributions from the HIMU, EM I, and DM components. Here, we present multiple sulfur isotope data on sulfide extracted from subaerial and submarine whole rocks associated with several Samoan volcanoes—Malumalu, Malutut, Upolu, Savaii, and Tutuila—that sample the full range of geochemical heterogeneity at Samoa and allow for an assessment of the S-isotope compositions associated with the different mantle components sampled by the Samoan hotspot. We observe variable S concentrations (10-1000 ppm) and δ34S values (-0.29‰ to +4.84‰ ± 0.3, 2σ). The variable S concentrations likely reflect weathering, sulfide segregation and degassing processes. The range in δ34S reflects mixing between the primitive mantle and recycled components, and isotope fractionations associated with degassing. The majority of samples reveal Δ33S within uncertainty of Δ33S=0 ‰ ± 0.008, suggesting Δ33S is relatively well mixed within the Samoan mantle plume. Important exceptions to this observation include: (1) a negative Δ33S (-0.018‰ ±0.008, 2σ) from a rejuvenated basalt on Upolu island (associated with a diluted EM I component) and (2) a previously documented small (but resolvable) Δ33S values (up to +0.027±0.016) associated with the Vai Trend (associated with a diluted HIMU component) [2]. The variability we observed in Δ33S is interpreted to reflect contributions of sulfur of different origins and likely multiple crustal protoliths. Δ36S vs. Δ33S relationships suggest all recycled S is of post-Archean origin. The heterogeneous S isotope values and distinct isotopic compositions associated with the various compositional trends confirms a prior hypothesis; unique crustal materials are heterogeneously delivered to the Samoan mantle plume and compositionally influence the individual groups of islands.

[1] Jackson et al. (2014), Nature; [2] Dottin et al. (2020), EPSL

How to cite: Dottin, J., Labidi, J., Jackson, M., and Farquhar, J.: Sulfur isotope evidence of geochemical zonation of the Samoan mantle plume, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6416, https://doi.org/10.5194/egusphere-egu21-6416, 2021.