Sulfur isotope characterization of primordial and recycled sources feeding the Samoan mantle plume

Mantle plumes, such as the one responsible for generating the Hawaiian Archipelago, represent a rare opportunity to indirectly sample the Earth's mantle. Geochemical studies of ocean island basalts (OIB) show that the mantle is chemically and isotopically heterogeneous at scales ranging from millimeters to thousands of kilometers (Hofmann, 2003). Volcanoes in the Hawaiian Islands are distributed along two subparallel geographical trends that are geochemically distinct (

Section: Introductionmentioning

confidence: 99%

Fine‐Scale Structure of Earth's Deep Mantle Resolved Through Statistical Analysis of Hawaiian Basalt Geochemistry

Weis

Harrison

McMillan

et al. 2020

“…Note that in Dottin et al. (2020b) AVON3‐63‐2 and AVON3‐70‐9 have Δ 33 S uncertainty of 0.016‰ as a result of shorter analytical sessions.…”

Section: Methodsmentioning

confidence: 93%

“…Recent work by Dottin et al. (2020b) identified slightly positive Δ 33 S at Vailulu‘u, associated with a dilute HIMU contribution, and demonstrate that the magnitude of the Δ 33 S signature is consistent with a post‐Archean recycled component (Dottin et al. 2020b).…”

Section: Introductionmentioning

confidence: 95%

Sulfur Isotope Evidence for a Geochemical Zonation of the Samoan Mantle Plume

Dottin

Labidi

Jackson

et al. 2021

Self Cite

Basalts from the Samoan volcanoes 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 (N = 16) associated with several Samoan volcanoes—Vailulu‘u, Malumalu, Malutut, Upolu, Savai‘i, and Tutuila—that sample the full range of geochemical heterogeneity at Samoa and upon exhaustive compilation of S‐isotope data for Samoan lavas, 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 (10–1,000 ppm) and δ34S values (−0.29‰ ± 0.30 to +4.84‰ ± 0.30, 2σ). The observed variable S concentrations are likely due to sulfide segregation and degassing processes. The range in δ34S reflects mixing between the mantle origin and recycled components, and isotope fractionations associated with degassing. The majority of samples reveal Δ33S within uncertainty of Δ33S = 0‰ ± 0.008. Important exceptions to this observation include: (a) a negative Δ33S (−0.018‰ ± 0.008, 2σ) from a rejuvenated basalt on Upolu island (associated with a diluted EM I component) and (b) previously documented small (but resolvable) Δ33S values (up to +0.027 ± 0.016) associated with the Vai Trend (associated with a diluted HIMU component). The variability we observed in Δ33S is interpreted to reflect contributions of sulfur of different origins and likely multiple crustal protoliths. Δ36S versus Δ33S relationships suggest all recycled S is of post‐Archean origin.

“…There is also no clear evidence that degassing can explain the change of Δ 33 S with δ 34 S from 0.515 by significant amounts. Although analyses of degassed OIB show shifts for δ 34 S, they show no significant Δ 33 S variations, even when large δ 34 S fractionations are produced (Beaudry et al, 2018; Dottin et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

“…The contribution of negative δ 34 S components at Mangaia is unusual. It contrasts with recycled components observed at Samoa (EM II) and Discovery (EM I) hotspots, where positive δ 34 S values are observed (Dottin et al, 2020;Labidi et al, 2013Labidi et al, , 2015. Another HIMU hotspot, the Canary Islands, also shows a mantle source with positive δ 34 S values (Beaudry et al, 2018), and MORBs that incorporate variable amounts of HIMU components (Sobolev et al, 2007) appear to be influenced by a source with δ 34 S = +3 ± 2‰ (Labidi et al, 2014;Labidi & Cartigny, 2016).…”

Section: Unusual δ 34 S In Himu Oibmentioning

confidence: 97%

Isotopic Evidence for Multiple Recycled Sulfur Reservoirs in the Mangaia Mantle Plume

Dottin

Labidi

Jackson

et al. 2020

Self Cite

Mangaia, an ocean island in the Cook-Austral volcanic chain, is the type locality for the HIMU mantle reservoir and has also been shown to exhibit evidence for recycled sulfur with anomalous δ 34 S and Δ 33 S that has been attributed an Archean origin. Here we report bulk S-isotope data from sulfide inclusions in olivine and pyroxene phenocrysts from one of the previously analyzed and four additional Mangaia basalts to further test for the prevalence of anomalous S in the HIMU mantle source feeding Mangaia. We document compositions that range from −5.13‰ to +0.21‰ (±0.3 2σ), +0.006‰ to +0.049‰ (±0.016 2σ), −0.81‰ to +0.69‰ (±0.3 2σ) for δ 34 S, Δ 33 S, and Δ 36 S, respectively. These data extend the range of measured compositions and suggest S-isotope heterogeneity in the HIMU mantle source at Mangaia. We show that S-isotope compositions of bulk sulfide in olivine is not in isotopic equilibrium with bulk sulfide in pyroxene from the same samples and that samples from a confined area (M4, M10, M12, and M13) in the northern central part of the island show a distinct covariation for δ 34 S and Δ 33 S. This isotopic variation (forming an array) suggests mixing of sulfur from two sources that were captured at different stages of crystallization by phenocrysts in the Mangaia HIMU sulfur endmember. Plain Language Summary The sulfur isotope composition of the mantle is heterogenous from crust formation and recycling continental and oceanic crust. Basalts, from an intraplate volcanic hotspot volcano in the Pacific Ocean, Mangaia, show isotopic evidence for hosting Archean-related sulfur that is sourced from a recycled oceanic crustal component. The prevalence of this Archean-related sulfur in the plume source that feeds Mangaia is not well constrained. In this work, we present sulfur isotope data on sulfur from minerals that crystallized deep in the magma chamber and identify a new, potentially younger, recycled sulfur source that demonstrates the diversity of materials mixing in the magma chamber prior to eruption.