Periodic Reporting for period 1 - VOLATILES_MERCURY (The fate of volatiles in magma on Mercury)
Reporting period: 2019-08-01 to 2021-07-31
24 successful high pressure-temperature experiments have been performed by gas-mixing furnace for 1 atm and piston-cylinder press for 0.5 – 4 GPa. The starting compositions are CaO-MgO-Al2O3-SiO2 + Na2O and CaO-MgO-Al2O3-SiO2 + S, and all experimental samples have been analysed by electron-microprobe (EMPA). Our current experimental results show that the Na2O or S can significantly decrease the solidus of Mercurian mantle over 80 C. This preliminary result significantly changed the dynamic numerical model of the evolution of Mercurian interior.
Task 2: Speciation, role and fate of volatiles (Sulfur and Carbon) on Mercury under highly reducing conditions
27 successful high pressure-temperature experiments focusing on S have been done by piston-cylinder press at the pressure of 1 – 4 GPa and the temperature of 1200 – 1600 C. The major and trace elements in our experimental samples have been analyzed by electron-microprobe (EMPA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), respectively. We did find the S-bearing phases (e.g. (Ca,Mg)S) at the extremely reduced condition, and the experimental temperature significantly affects the solubility of S in a mercurian conditions. Unfortunately, we have not done the Raman measurements for testing the speciation of S in our experiments or the role of C under highly reducing conditions, due to the influence of Covid pandemic.
Task 3: Distribution of trace elements (U, Th and K) in the mantle of Mercury
19 successful high pressure-temperature experiments have been performed by the piston-cylinder press at the pressure of 0.5 – 4 GPa and the temperature of 1200 – 1600 C. Some of experiments have been analysed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The other experiments have not been measured, due to the pandemic and the travel ban to Germany for LA-ICP-MS measurement. Although the current experimental data show a result consistent with what we expected, more experiments and data are needed to accomplish this task because the effects of S concentration and oxygen fugacity on partitioning of those elements are still unclear.
This project was rooted in igneous petrology and in the combination of experimental petrology, geochemical analyses, numerical and thermodynamic modelling, and spacecraft measurements of the surface of Mercury acquired by MESSENGER. The experimental strategy and the interpretations of data also strongly rely on geophysical measurements for the internal structure of Mercury. Our experiments can also be used for the calibration of the MERTIS instrument (Mercury Radiometer and Thermal Imaging Spectrometer) installed on the Mercury Planetary Orbiter of the BepiColombo spacecraft (to be launched to Mercury in October 2018). We discussed with the Principal Investigator Harald Hiesinger (University of Münster, Germany) and co-Principal Investigator Jörn Helbert (DLR Institut für Planetenforschung, Berlin, Germany) and shared our experiments' data that have relevant compositions and mineralogy for the surface of the planet. MERTIS is an infrared imaging spectrometer and these wavelengths have a high potential for mineral identification because it is in this region where the major rock-forming minerals have their fundamental vibration bands.