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 δ34S and Δ33S 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 δ34S, Δ33S, and Δ36S, 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 δ34S and Δ33S. 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.
The origin, evolution, and cycling of volatiles on the Moon are established by processes such as the giant moon forming impact, degassing of the lunar magma ocean, degassing during surface eruptions, and lunar surface gardening events. These processes typically induce mass‐dependent stable isotope fractionations. Mass‐independent fractionation of stable isotopes has yet to be demonstrated during events that release large volumes of gas on the moon and establish transient lunar atmospheres. We present quadruple sulfur isotope compositions of orange and black glass beads from drive tube 74002/1. The sulfur isotope and concentration data collected on the orange and black glasses confirm a role for magmatic sulfur loss during eruption. The Δ33S value of the orange glasses is homogenous (Δ33S = −0.029‰ ± 0.004‰, 2SE) and different from the isotopic composition of lunar basalts (Δ33S = 0.002‰ ± 0.004‰, 2SE). We link the negative Δ33S composition of the orange glasses to an anomalous sulfur source in the lunar mantle. The nature of this anomalous sulfur source remains unknown and is either linked to (a) an impactor that delivered anomalous sulfur after late accretion, (b) sulfur that was photochemically processed early during lunar evolution and was transported to the lunar mantle, or (c) a primitive sulfur component that survived mantle mixing. The examined black glass preserves a mass‐dependent Δ33S composition (−0.008‰ ± 0.006‰, 2SE). The orange and black glasses are considered genetically related, but the discrepancy in Δ33S composition among the two samples calls their relationship into question.
more » « less- Award ID(s):
- 2052944
- NSF-PAR ID:
- 10470821
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Planets
- Volume:
- 128
- Issue:
- 2
- ISSN:
- 2169-9097
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Basalts from the Samoan volcanoes sample contributions from all of the classical mantle endmembers, including extreme EM II and high3He/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. -
Volcanic rocks erupted among Pitcairn seamounts sample a mantle plume that exhibits an extreme Enriched Mantle-1 signature. The origin of this peculiar mantle endmember remains contentious, and could involve the recycling of marine sediments of Archean or Proterozoic ages, delaminated units from the lower continental crust, or metasomatized peridotites from a lithospheric mantle. Here, we report the sulfur multi-isotopic signature (32S, 33S, 34S, 36S) of 15 fresh submarine basaltic glasses from three Pitcairn seamounts. We observe evidence for magmatic degassing of sulfur from melts erupted ∼2,000 meters below seawater level (mbsl). Sulfur concentrations are correlated with eruption depth, and range between 1300 ppm S (collected ∼ 2,500 mbsl) and 600 ppm S (∼2,000 mbsl). The δ34S values can be accounted for under equilibrium isotope fractionation during degassing, with αgas-melt between 1.0020 and 1.0001 and starting δ34S values between −0.9‰ and +0.6‰. The δ34S estimates are similar or higher than MORB signatures, suggesting the contribution of recycled sulfur with a ∼ 1‰ 34S enrichment compared to the Pacific upper mantle. The Δ33S and Δ36S signatures average at +0.024±0.007‰ and +0.02±0.07‰ vs. CDT, respectively (all 1σ). Only Δ33S is statistically different from MORB, by +0.02‰. The Δ33S enrichment is invariant across degassing and sulfide segregation. We suggest it reflects a mantle source enrichment rather than a high-temperature fractionation of S in the basalts. Despite the small magnitude of the 33S-36S variations, our data require a substantial amount of recycled sulfur overwhelm the Pitcairn mantle source. We show that models involving metasomatized peridotites, lower crust units, or Archean sediments, may be viable, but are restricted to narrow sets of circumstances. Instead, scenarios involving the contribution of Proterozoic marine sediments appear to be the most parsimonious explanation for the EM-1 signature at Pitcairn.more » « less
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Abstract Lunar impact glasses, formed during impact events when the regolith is quenched during the ejecta's ballistic flight, are small samples whose information can lead to important advances in studies of the Moon. For example, they provide evidence that constrains both the compositional evolution of the lunar crust and the timing of the lunar impact flux starting at ~4,000 million years ago. They are abundant in the lunar regolith and retain geochemical information that tells us where and when they formed. Thus, they provide important details about areas of the Moon both sampled and not sampled by Apollo or Luna missions or lunar meteorites. Additionally, as a result of these glasses possessing a chemical memory of formation location and age, studies of lunar impact glasses provide a foundation on which to conduct studies of impact glasses from other planetary bodies. A summary of past and current lunar impact glass investigations, using glasses from the Apollo 11, 12, 14, 15, 16, and 17 regoliths, along with plans for future work, will be presented.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1029/2022JE007597
