From Stromboli ashes to corrensite by hydrothermal synthesis: Hydrogeological inputs into Mars history

The detection of mixed-layered clays is well known on Mars and evidences the presence of water on the planet. To understand the processes related to the formation of these mixed-layered clays on Mars, we performed a set of hydrothermal syntheses on basaltic ash of Stromboli volcano (Southern Italy), selected for its composition similar to Martian rocks. Syntheses were carried out by opportunely modulating the experimental conditions. Trials were performed at constant pH = 5, with pressure of 0.1–50 Mpa and temperatures ranging from 150 °C to 350 °C, and runs lasting from 5 to 31 days. In specific conditions described herein, corrensite crystals (mixed-layered clays) were produced. Optical microscope (OM), Powder X-Ray Diffraction (PXRD) and Scanning and Transmission Electron Microscopy, both combined with Energy Dispersive Spectroscopy (SEM/EDS; TEM/EDS), wavelength-dispersive electron probe microanalysis (WDS/EPMA), X-ray fluorescence (XRF), thermogravimetric and differential scanning calorimetry (TG/DSC), Fourier transform infrared spectroscopy (FTIR/ATR) and micro-Raman spectroscopy (μR) were used for a detailed mineralogical, chemical and morphological characterization before and after hydrothermal alteration. The findings that emerge point out that corrensite formed on Mars probably originated from the alteration of the basaltic rocks at a low grade of hydrothermal metamorphism in a Fe(II) enriched environment.