Work Description

Date: 5 August, 2024

Dataset Title: Data of the paper "Sulfur Outgassing and In-gassing in Lunar Orange Glass Beads and Implications for 33S “Anomaly” in the Moon"

Dataset Creators: Xue Su, Youxue Zhang, and Yang Liu

Dataset Contact: [email protected]

Funding: 80NSSC23K1297 (NASA), JPL’s Strategic University Research Partnerships (SURP) program

Key Points:
- this is first discovery of "U" or "W" shaped S profiles across lunar 74220 orange beads;
- this work reveals the role of in-gassing in shaping sulfur isotope signatures in lunar volcanic glass beads;
- this work proposes a scenario to reconcile the current Δ33S data on lunar volcanic glass beads;
- this work estimates the Δ33S value of the eruption plume during lunar orange glass eruptions.

Research Overview:
Our recent investigations have discovered inward diffusion (in-gassing) of moderately volatile elements (MVEs; e.g., Na, K and Cu) from volcanic gas into volcanic beads/droplets. In this work, we examine the distribution of sulfur in lunar orange glass beads. Our analyses reveal that sulfur exhibits a non-uniform distribution across the beads, forming "U" or "W" shaped profiles typical of in-gassing. A model developed to assess sulfur contributions from different sources (original magmatic sulfur versus atmospheric in-gassed sulfur) in the orange beads indicates that atmospheric sulfur in-gassed during eruption contributes approximately 9–24% to the total sulfur content of an orange bead, averaging around 16%. This in-gassed sulfur is derived from the eruption plume, where atmospheric sulfur could undergo photochemical reactions induced by UV light, leading to mass independent fractionation and a distinct sulfur isotope signature.
Interestingly, a recent study discovered a small mass independent isotope fractionation of sulfur in lunar orange glass beads in drive tube 74002/1 and a lack of such mass independent isotope fractionation in black glass beads in the same lunar sample. This finding contrasts with sulfur in lunar basalts, which typically exhibit mass dependent fractionation. With our work, the observed mass independent fractionation signal in sulfur isotopes of orange beads can be attributed to the in-gassing of photolytic sulfur in the optically thin part of the eruption plume where UV light can penetrate. Using the sulfur isotope data of lunar orange beads, we estimate that the Δ33S value of atmospheric sulfur is approximately −0.18‰. Our study provides new insights into the complex dynamics of volatile elements in lunar volcanic processes, highlighting the role of in-gassing in shaping sulfur isotope signatures in volcanic glass beads.

Methodology:
Four spherical orange glass beads from pristine lunar sample 74220,892 and 74220,949 are studied for sulfur in this work. The beads were first handpicked from 74220 soils under optical microscope and then separately loaded onto glass slides with epoxy for polishing to expose the geometric center (largest cross section area). We used epoxy to avoid rounding off the edge of the beads during polishing. The exposed cross sections were examined for texture homogeneity under a JEOL JSM-7800FLV field-emission Scanning Electron Microscope (FE-SEM) at the University of Michigan. Beads that are nearly spherical without noticeable crystallites were extracted from epoxy, cleaned, and loaded into an indium mount for further composition measurements.
Major and minor element composition variations across the polished sections of the orange beads are determined using a CAMECA SX-100 Electron Microprobe (EMP) at the University of Michigan. A 10 nA focused beam with 15 kV accelerating voltage is used during the analyses. Measured elements include Si, Ti, Al, Cr, Fe, Mn, Mg, Ca, Na. Beads with symmetric Na concentration profiles were chosen for further study of S concentration profiles.
To measure the sulfur concentration profiles from rim to rim across the center, a Cameca Nano Secondary Ion Mass Spectrometry (NanoSIMS) 50L is used at the California Institute of Technology. A Cs+ primary beam of +8 kV is used to raster at 2×2 µm square area with signals collected from the central 1×1 µm. Cs+ beam current onto the sample surface is 5–20 pA. Negatively charged secondary 32S- ions are collected with 18O- (and 30Si- in a few sessions) as internal standards to correct for instrumental fluctuation. We pre-sputter for 290 s before analysis and collect 300–500 cycles for each point. The profiles are measured across the polished sections of the beads with a step size of 5–10 µm.

Instrument specifications: SEM, EMPA, NanoSIMS

The span of time that the data were collected and processed: 2 years (2022-2024)

Files contained here:
- An excel file named "Su_et_al._GCA_supplementary file" which contains Table S1 to Table S3 of the paper.
- An excel file named "Su_et_al._GCA_Data_for_Figures" which contains the data that are used for figures in the paper.
- A zip file named "Su_et_al._GCA_python codes" which contains the python codes that are used for modeling in the paper with two data files to be read by the codes. List of scripts included in the folder:
- step1_Na_fitting.py and step1_Solver_Na.py: fit Na profiles and obtain the cooling time scales of the bead.
- step2_S_fitting_grid_search.py and step2_Solver_S.py: use grid search to search for parameters that best fit S profiles. The output results are stored in Grid_search_a0_b0_C0_aD_misfits_results.npy.
- Na_S_loss_gain.py: calculate Na and S loss and gain during the outgassing and in-gassing processes.
- Na_data.xlsx and S_data.xlsx: data files to be read. To read the files, update ‘file_dir’ to your computers file path.

Software needed: to run the python scripts, these packages are needed: numpy, pandas, matplotlib.pyplot, scipy.interpolate, numba.

Related publication(s):
Su, X., Zhang, Y., Liu, Y. (2024) Sulfur Outgassing and In-gassing in Lunar Orange Glass Beads and Implications for 33S “Anomaly” in the Moon. (under review)

Use and Access:
This data set is made available under an Attribution-NonCommercial 4.0 International license (CC BY-NC 4.0).

To Cite Data:
Su, X., Zhang, Y., Liu, Y. (2024) Data of the paper "Sulfur Outgassing and In-gassing in Lunar Orange Glass Beads and Implications for 33S “Anomaly” in the Moon" [Data set], University of Michigan - Deep Blue Data.