Work Description

Date: 20 February, 2025

Dataset Title: Data of the paper "Cooling history and Evolution Dynamics of Green Glass Beads during Lunar Fire-Fountain Eruptions: Insights from Na, K and Cu Distributions"

Dataset Creators: Xue Su, Youxue Zhang, Yang Liu, and Robert M. Holder

Dataset Contact: [email protected]

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

Key Points:
- Lunar green glass beads are found to have increased Na, K and Cu near bead surfaces, indicating in-gassing.
- By modeling the Na and Cu concentration profiles, cooling histories of individual lunar green beads are constrained.
- LA-ICP-MS mapping of one green bead also shows features that suggest collision of melt droplets during the formation.
- Compared to orange beads, the eruption plume during green bead eruptions may have evolved and dissipated more quickly.

Research Overview:
Volcanic glass beads on the Moon have traditionally been thought to only record volatile loss during pyroclastic eruptions. However, recent discoveries have shown that lunar orange glass beads, representing primitive high-Ti basalts, experienced both outgassing and in-gassing of volatile elements such as Na, K, Cu, and S. In this work, we examine lunar green glass beads from sample 15421 and 15366, representing primitive very-low-Ti basalts, for the distribution of Na, K and Cu using EMP analyses and LA-ICP-MS mapping. It is found that all studied lunar green beads show increased Na, K and Cu concentrations near bead surfaces, indicative of in-gassing. A quantitative model is developed to simulate the concentration evolution of Na and Cu in individual green glass beads during eruption and cooling. The presence of similar in-gassing diffusion profiles of volatile elements in beads from different eruptions indicates a common behavior of lunar volcanic gas. In addition to volatile in-gassing, LA-ICP-MS mapping of Na and K in one green bead from sample 15366 shows features suggesting collision of melt droplets during the fire-fountain eruption, revealing more details in the dynamic aspects of lunar fire-fountain eruptions. Compared to orange glass beads, the varying boundary conditions of green glass beads during formation may suggest that their eruption plume evolved and dissipated more rapidly, potentially linked to changes in the global lunar atmosphere.

Methodology:
In total, six green glass beads from Apollo 15421,8 and two green glass beads from clod 15366,14 were studied in this work. Spherical beads of various sizes were handpicked under optical microscope. The picked beads were processed following the procedure in Su et al. (2023) which is briefly described below. After being embedded in epoxy, the beads were polished to reveal central cross sections. The polished beads were then examined for textural homogeneity using a JEOL JSM-7800FLV Field-Emission Scanning Electron Microscope (FE-SEM) at the University of Michigan. Completely glassy beads without crystallites or bubbles were selected to be measured for major and minor element compositions and mapped for the distributions of Na, K and Cu.
The determination of major and minor element compositions of the green beads used a CAMECA SX-100 Electron Microprobe (EMP) at the University of Michigan. Major and minor elements include Si, Ti, Al, Cr, Fe, Mn, Mg, Ca, Na and K were measured using a 10 nA focused beam with an accelerating voltage of 15 kV in focus mode.
The distributions of Na, K and Cu in the green beads were determined by elemental mapping using Laser-Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) at the University of Michigan following the procedure established in Su et al. (2023). Green beads from sample 15421 and 15366 were analyzed in two different sessions. In addition to the elements of interest, Al and/or Fe were also included during the analysis as an internal standard. Samples were ablated using an ESI NWR193 excimer laser connected to an Agilent 7900 ICP-MS. For both samples, the fluence was 3.5 J/cm2 and beam size was an 8 μm square. Isotope integration times on the ICP-MS and laser scan speeds were set such that measurement spacing corresponded exactly to the beam size (8 μm). Laser repetition rates were set sufficiently high to minimize signal pulsing, low enough that the depth of ablation should be comparable to the lateral spatial resolution of the maps (~8 μm, assuming ~0.1 μm removal per shot), and an integer factor of the duty cycle to prevent aliasing of the signal if any laser pulsing were still present in the ICP-MS counts (e.g., Van Elteren et al., 2019). For sample 15421, the integration times were 400 ms for 23Na, 39K and 63Cu and 50 ms for 27Al. The scan speed was 4 μm/s and the repetition rate was 40 Hz. For sample 15366, the integration times were 450 ms for 23Na, 39K, and 63Cu and 450 ms for 57Fe with an integration time of 242 ms. The scan speed was 5 μm/s and the repetition rate was 60 Hz. Rasters were constructed by consecutive line-scans. Pre-ablation cleaning shots were performed before each line-scan to remove any surface contaminations.

Instrument specifications: SEM, EMPA, LA-ICP-MS

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._JGR_supplementary file" which contains Table S1 to Table S3 of the paper.
- A folder named "BSE images of GBs" which contains the BSE images of the studied green glass beads from sample 15421 and 15366.
- A folder named "LA-ICP-MS mapping raw data" which contains the raw mapping data of isotope Na23, Al27, K39, Fe57 and Cu63 signal in the form of count per second (cps) in each pixel. "GN" or "GNGB" represents "GreeN Glass Bead" and the label following it represents the name of each green glass bead sample. For example, "GN-G2 Cu63_CPS matrix.csv" means that this csv file contains the Cu63 isotope signals (cps) in the form of a matrix of the green glass bead named GN-G2.
- A folder named "python codes" that contains the python codes that are used for modeling in the paper with two data files to be read by the codes (one for Na and one for Cu). List of files included in the folder:
- Fitting_15421_2GB_G3&H4.py: fit Na and Cu profiles and obtain the cooling time scales of green glass bead GN-G3 and GN-H4 in sample 15421.
- Fitting_15421_4GB_except_G3_H4.py: fit Na and Cu profiles and obtain the cooling time scales of the other four studied green glass beads in sample 15421.
- Fitting_15366_1GB_GNGB3.py: fit Na and Cu profiles and obtain the cooling time scale of the green glass bead GNGB3 in sample 15366.
- Solver_Na_Cu.py: to be called by the fitting scripts to calculated the predicted profiles.
- Na_EMPA+LAICPMS.xlsx and Cu_LAICPMS.xlsx: data files to be read.

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. and Holder, R.M. (2025) Cooling history and Evolution Dynamics of Green Glass Beads during Lunar Fire-Fountain Eruptions: Insights from Na, K and Cu Distributions. (To be submitted)

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. and Holder, R.M. (2025) Data of the paper "Cooling history and Evolution Dynamics of Green Glass Beads during Lunar Fire-Fountain Eruptions: Insights from Na, K and Cu Distributions" [Data set], University of Michigan - Deep Blue Data.