Periodic Reporting for period 1 - SuChaMa (Sulfur and Chalcophile elements in the Mantle: An Experimental Investigation of the Sulfur Cycle in the Terrestrial Interior)
Reporting period: 2021-11-01 to 2023-10-31
The abundance and distribution of sulfur (S) is of key importance for the occurrence and interpretation of geochemical processes. For example, the abundance and distribution of S controls potential sulfide or sulfate precipitation from silicate melts and therefore the cycles of sulfide/sulfate-loving elements such as Se, Te, Bi, the composition and properties of volcanic gases and the composition of planetary metallic cores. On the other hand, the measurement of sulfur in ancient (extra)-terrestrial rocks provides important clues to the processes of volatile loss and delivery in the early solar system. Prior to the project, the distribution of S in the deep interior and in small planetesimals were not well constrained. The main objectives / research questions from the SuChaMa project were therefore:
1. How much S can be stored in the deep terrestrial interior? The project has successfully studied the potential of S storage in the deep Earth by sulfide liquids, by analyzing and interpreting previous experiments at pressures and temperatures relevant to the deep Earth. The sulfur content at sulfide saturation was quantified and used to assess whether sulfide liquid saturation during differentiation of the Earth would be a likely process. The interpretation of previous experimental data showed that it is unlikely that a sulfide liquid segregated from the terrestrial silicate magma ocean in its early history.
2. How much S is lost during planetary accretion from metal-rich planetesimals? Another important aspect of the project was to investigate the potential evaporative loss from S from metal-rich planetesimals. For this purpose, high-temperature evaporation experiments were performed in a furnace, at vacuum and room pressures. Geochemical analyses of the run products provided the first experimental constraints on S evaporation from metal melts. The experiments show that S behaves volatile, but significantly less so as commonly assumed.
The geochemical interpretation of experiments and the conducted evaporation experiments were not only novel, they were thus critical in quantifying the flux of S in the terrestrial planets.
The Institute for Mineralogy at the University of Münster provided the much-needed modern and reliable experimental and analytical equipment, as well as the outstanding technical and scientific personnel. The project was therefore an excellent match, and it is expected that the project results reinforce the reputation of the University of Münster as one of Europe’s leading institutes for application of experimental petrology to planetary science.
1. How much S can be stored in the deep terrestrial interior? The project has successfully studied the potential of S storage in the deep Earth by sulfide liquids, by analyzing and interpreting previous experiments at pressures and temperatures relevant to the deep Earth. The sulfur content at sulfide saturation was quantified and used to assess whether sulfide liquid saturation during differentiation of the Earth would be a likely process. The interpretation of previous experimental data showed that it is unlikely that a sulfide liquid segregated from the terrestrial silicate magma ocean in its early history.
2. How much S is lost during planetary accretion from metal-rich planetesimals? Another important aspect of the project was to investigate the potential evaporative loss from S from metal-rich planetesimals. For this purpose, high-temperature evaporation experiments were performed in a furnace, at vacuum and room pressures. Geochemical analyses of the run products provided the first experimental constraints on S evaporation from metal melts. The experiments show that S behaves volatile, but significantly less so as commonly assumed.
The geochemical interpretation of experiments and the conducted evaporation experiments were not only novel, they were thus critical in quantifying the flux of S in the terrestrial planets.
The Institute for Mineralogy at the University of Münster provided the much-needed modern and reliable experimental and analytical equipment, as well as the outstanding technical and scientific personnel. The project was therefore an excellent match, and it is expected that the project results reinforce the reputation of the University of Münster as one of Europe’s leading institutes for application of experimental petrology to planetary science.
High-temperature evaporation experiments were performed at the Institute for Mineralogy at the University of Münster to investigate the volatile behavior of S and other elements during melting of metal-rich planetesimals in the early solar system. Synthetic metal and sulfide starting powders were mixed with volatile trace elements (e.g. S, Se, Te) in graphite capsules which in turn were placed within a large graphite bucket on a sample hanger, made with W-Re wire. The sample and hanger were then placed in the furnace, and the temperature and pressure were regulated using an Eurotherm and vacuum pump, respectively. Experiments were conducted at different run times ar a given pressure and/or temperature. Samples were rapidly quenched by first removing the vacuum (if needed) and/or gas flow after which the graphite bucket with sample were held in a water-bearing open container. Each sample was mounted in epoxy resin and polished, after which they were analyzed using electron microprobe and/or laser ablation - inductively coupled plasma mass spectrometry (LA-ICPMS). The electron microprobe was used to quantify the major element abundances in the samples, whereas LA-ICPMS was used to quantify the concentrations of trace elements (up to 0.1 ppm). In some cases, back-scattered electron images were used to obtain representative bulk compositions of the entire run product. The novel experimental data was used to assess the loss of S and other volatiles from metal-rich planetesimals prior to their accretion to the terrestrial planets. This was done by comparing the post-experimentally measured volatile element content of the evaporated samples to the original, undegassed starting composition powders. The experimental results were then compared with geochemical measurements of iron meteorites from the literature to assess the process(es) that were responsible for the depletion of S and other volatile elements from the latter meteorites. At the same time, previously obtained experimental data focused on the sulfur content at sulfide saturation were interpreted and used for geochemical modeling to assess the deep Earth sulfur cycle. The results were presented at the Lunar and Planetary Science Conference 2023. One manuscript has been published in Geochemical Perspective Letters and one is in preparation.
Although the SuChaMa project constitutes fundamental research, insights into the sulfur cycles of terrestrial planets are highly relevant to sulfide ore petrogenesis, the distribution of critical elements that are commonly sulfide-loving as well as to the field of metallurgy and material science. The experimental evaporation results of the project could therefore be used in future studies of metal and sulfide industrial processing and to industrial procedures. Another key result of the SuChaMa project was to further enforce the role of the University of Münster as a key player in the application of experimental petrology to planetary science. This will contribute to the importance of German and overall European research in the world.