Gas-mediated trace element incorporation into rhyolite-hosted topaz: A synchrotron microbeam XAS study

Schaub, D.R.; Northrup, Paul; Nekvasil, Hanna; Catalano, Tristan; Tappero, Ryan

doi:10.2138/am-2022-8417

Cited by 2 publications

(2 citation statements)

References 38 publications

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“…(C) Mn K-edge μ-XANES from eight Mn-rich spots in the upper section of PRR50504 (combined in the green spectrum) and a Mn-carbonate standard (rhodochrosite, black spectrum). Both spectra have weak pre-edge peak at 6539eV, and an edge position at 6549eV indicative of Mn 2+ species (Schaub et al, 2023); the double peak structure is characteristic of rhombohedral carbonate (Lee et al, 2002).…”

Section: Manganous Brine Formation Tied To Ice Dynamic Processesmentioning

confidence: 99%

Antarctic Subglacial Trace Metal Mobility Linked to Climate Change Across Termination III

Piccione,

Blackburn,

Northrup

et al. 2024

Preprint

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Abstract. Antarctic meltwater is a significant source of iron that fertilizes present-day Southern Ocean ecosystems and may enhance marine carbon burial on geologic timescales. However, it remains uncertain how this nutrient flux changes through time, particularly in response to climate, due to an absence of geologic records detailing trace metal mobilization beneath ice sheets. In this study, we present a 25 kyr record of aqueous trace metal cycling beneath the East Antarctic Ice Sheet measured in a subglacial chemical precipitate that formed across glacial termination III (TIII). The deposition rate and texture of this sample describe a shift in basal meltwater flow following the termination. Alternating layers of opal and calcite deposited in the 10 kyr prior to TIII record centennial-scale subglacial flushing events, whereas reduced basal flushing resulted in slower deposition of a trace metal-rich (Fe, Mn, Mo, Cu) calcite in the 15 kyr after TIII. This sharp increase in calcite metal concentrations following TIII indicates that diminished subglacial meltwater flow restricted the influx of oxygen from basal ice melt to precipitate-forming waters, causing dissolution of redox-sensitive trace metals from the bedrock substrate. These results are consistent with a possible feedback between orbital climate cycles and Antarctic subglacial iron discharge to the Southern Ocean, whereby heightened basal meltwater flow during terminations supplies oxygen to subglacial waters along the ice sheet periphery, which reduces the solubility of redox sensitive elements. As the climate cools, thinner ice and slower ice flow reduce basal meltwater production rates, limiting oxygen delivery and promoting more efficient mobilization of subglacial trace metals. Using a simple model to calculate the concentration of Fe in Antarctic basal water through time, we show that the rate of Antarctic iron discharge to the Southern Ocean is highly sensitive to this heightened mobility, and may therefore, increase significantly during cold climate periods.

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Section: Manganous Brine Formation Tied To Ice Dynamic Processesmentioning

confidence: 99%

Antarctic Subglacial Trace Metal Mobility Linked to Climate Change Across Termination III

Piccione,

Blackburn,

Northrup

et al. 2024

Preprint

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“…Figure10. (A) Mn K-edge µXANES of three representative spots on the two Ryugu samples are compared to reference spectra for Mn foil, Mn 2+ (sulfate), Mn 3+ (bixbyite Mn 2 O 3 ), and Mn 4+ (pyrolusite, MnO 2 ) (reference spectra from[12]). The absorption edge (initial rise) position in energy is characteristic of oxidation state and shows that Mn in these Ryugu grains is Mn 2+ as marked by the vertical dotted line.…”

mentioning

confidence: 99%

Chemistry in Retrieved Ryugu Asteroid Samples Revealed by Non-Invasive X-ray Microanalyses: Pink-Beam Fluorescence CT and Tender-Energy Absorption Spectroscopy

Northrup,

Tappero,

Glotch

et al. 2024

Geosciences

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The Hayabusa2 space mission recently retrieved 5.4 g of material from asteroid Ryugu, providing the first direct access to pristine material from a carbonaceous asteroid. This study employs a novel combination of non-invasive synchrotron X-ray techniques to examine microscale chemistry (elemental distributions and element-specific chemical speciation and local structure) inside Ryugu grains without physically cutting the samples. Manganese primarily occurs in carbonate: Mn-bearing dolomite with minor earlier ankerite. Iron sulfides present as large single grains and as smaller particles in the finer-grained matrix are both predominantly pyrrhotite. At the 5 μm scale, Fe sulfides do not show the mineralogical heterogeneity seen in many carbonaceous meteorites but exhibit some heterogeneous localized oxidation. Iron is present often as intergrowths of oxide and sulfide, indicating incomplete replacement. Trace selenium substitutes for S in pyrrhotite. Copper is present as Fe-poor Cu sulfide. These results demonstrate multiple episodes of fluid alteration on the parent body, including partial oxidation, and help constrain the sequence or evolution of fluids and processes that resulted in the current grain-scale mineralogical composition of Ryugu materials.

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Gas-mediated trace element incorporation into rhyolite-hosted topaz: A synchrotron microbeam XAS study

Cited by 2 publications

References 38 publications

Antarctic Subglacial Trace Metal Mobility Linked to Climate Change Across Termination III

Antarctic Subglacial Trace Metal Mobility Linked to Climate Change Across Termination III

Chemistry in Retrieved Ryugu Asteroid Samples Revealed by Non-Invasive X-ray Microanalyses: Pink-Beam Fluorescence CT and Tender-Energy Absorption Spectroscopy

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