A Laboratory Simulation Experiment of Hydrothermal Processes on Mars

Hydrothermal processes on Mars: It has been suggested that hydrothermal process may have been active in the history of Mars[1]. This concept is supported by three lines of evidences: (1) widespread evidences of volcanic activity on Mars; (2) high levels of WEH (water-equivalent-hydrogen) found in two large equatorial regions on Mars (ODY_NS) [2]; (3) The ground ice excavated by meteorite impacts as observed by MRO_HiRISE and confirmed by MRO_CRISM [3]. Heat from volcanic activity interacting with ground water or ice could produce hydrothermal activity. The first surface confirmation of hydrothermal activity on Mars was made by Spirit, through exploration around the Home Plate area in Gusev Crater [4]. Amorphous silica and variety of sulfates were identified there and could be produced as secondary minerals by hydrothermal activity. In order to gain a better understanding on the hydrothermally produced secondary minerals under Mars relevant atmospheric conditions, especially their precipitation sequences and the compositional and structural details of the minerals and mineral assemblages, we designed a set of hydrothermal simulation experiments in laboratory under well controlled environmental conditions. This abstract describes the chemical and mineralogical characters of starting basalt and mineralogical characters of first set of experimental products. Laboratory Hydrothermal Simulation Experiment: Different from previous studies [5,6,7,8], our experiments has two characters: (1) the use of an oxygen-poor environment: a dry CO2 200 (purity 99.9%) environment (>1 atm); (2) the use of three temperature ranges to separate the produced secondary minerals. The experiment was conducted in three steps: (1) to react basaltic sand with acidic fluids (H2SO4: HCl in 4:1 molar ratio) with four different densities (5, 10, 15, 20%) and at two fluid to sand (2:1 and 10:1) ratio at 90C; (2) to separate the fluids from the sand after 1,3,10 days reactions; (3) to allow precipitation to occur in the decanted fluids at 50C; (4) to separate the precipitated solid; (5) to evaporate the residual fluid at room T. Every step of the experiment except (5) was conducted in a dry CO2 environment (>1 atm). A variety of analytical methods including EMP,SEM, ICP-MS, Raman, XRD, NIR & MIR spectroscopy are planned to examine the initial, middle and final reaction products. There are 20 vials of samples reacted at different conditions, that produced about one hundred samples, including reaction residues from 90C experiments, precipitated solids from 50C brines and the decanted fluids, and evaporated minerals from residual fluid at room T. The starting material is basaltic rock HP003, whose chemical composition (including compositional zoning) and surface morphology have been studied by EMP analysis. This sample was collected from a recent PuuOo flow of the Kilauea volcano in Hawaii. For our experiment, a piece of HP003 was crushed, ground, and sieved. The basaltic sand with size 250 m < d < 850 μm was used. Chemistry and mineralogy of the starting Basalt: We made EMP analysis on a polished HP003 basalt chip. The piece of sample was put in epoxy, polished with a smallest of 5m abrazine. Then the sample was carbon-coated and sent to make EMP analysis. The result of EMP analysis shows that HP003 includes great amount of glass, pyroxene, and plagioclase. Olivine was not report in EMP analysis, yet rare olivine has been observed with Raman measurements. The basalt is rich in Ca, Na, Fe, Mg, Al and Ti. We calculated the feldspar stoichiometry in the system An-AbOr based on EMP analysis, which shows an enrichment in anorthite CaAl2Si2O8 (71%), albite NaAlSi3O8 (28%), and poor in orthoclase KAlSi3O8 (0.5%). In addition, the pyroxene stoichiometry in the system Wo-En-Fs was calculated. It shows a large proportion of enstatite Mg2Si2O6 (55%), greater than wollastonite Ca2Si2O6(30%), and than ferrisilite Fe2Si2O6(15%).