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Oxidative Weathering of Olivine by Chlorate and Bromate: Implications for Phyllosilicate Formation on Mars.

Session: Advancing Mineral Science and Exploring Planetary Surfaces: In Honor of MSA Dana Medalist, Elizabeth B. Rampe (Posters)

Presenting Author:

Zoe Zoesch-Weigel

Authors:

Zoesch-Weigel, Zoe¹, Brancaleon, Elena Rose², Schoenenberger, Amy Rose³, Malesky, Lauren Rose⁴, Mitra, Kaushik Rose⁵

(1) Department of Earth and Planetary Science, University of Texas at San Antonio, San Antonio, Texas, USA, (2) Department of Earth and Planetary Science, The University of Texas at San Antonio, San Antonio, TX, USA, (3) Department of Earth and Planetary Science, The University of Texas at San Antonio, San Antonio, TX, USA, (4) Department of Earth and Planetary Science, The University of Texas at San Antonio, San Antonio, TX, USA, (5) Department of Earth and Planetary Science, The University of Texas at San Antonio, San Antonio, TX, USA,

Abstract:

Numerous studies of Mars surface mineralogy have revealed the prevalence of ferric iron [Fe(III)] minerals, such as iron oxides (e.g., hematite), oxyhydroxides (e.g., goethite), sulfates (e.g., jarosite), and clay minerals (e.g., nontronite). These iron mineral phases can be produced through near-surface aqueous alteration of primary ferrous iron mineral phases (e.g., olivine, pyroxene) at both low temperature (T<50°C) and hydrothermal conditions (T ~ 50 to 200°C). Several theoretical and experimental studies have reviewed the potential of dissolved oxygen, ultraviolet radiation, and other common dissolved anions as oxidative agents of ferrous minerals. Recent studies have demonstrated that oxyhalogen compounds, mainly chlorate and bromate, are highly effective oxidizing agents in Mars-relevant fluids.

Although oxyhalogen oxidation has been studied for dissolved ferrous iron, pyrite, pyrrhotite, and magnetite, no studies have examined olivine alteration despite its abundance in key Mars regions, like Jezero crater. This study investigates the aqueous alteration of olivine by chlorate and bromate. Terrestrial olivine end-members, forsterite and fayalite, in a Mars-relevant solution containing background fluids of MgCl2 or MgSO4 salt solutions between pH 3 and 10 were studied. Due to the slow dissolution rates of olivine occurring on a scale of tens to thousands of years at room temperature, experiments were conducted at 95°C to simulate hydrothermal conditions that could have occurred during periods of volcanism or following a meteorite impact. We conducted experiments in an anaerobic chamber, and olivine alteration was determined as a function of the oxidant type, initial pH, and background fluid. Experimental solutions were kept in an oven for approximately 50 days and 90 days at 95°C.

Changes in the colors of the solutions demonstrate that over a 50- and 90-day period, forsterite and fayalite underwent alteration following exposure to bromate and chlorate. Acidic conditions enhanced the rate of reaction, leading to a deep rust color in these solutions. Alkaline solutions also showed a change in coloration due to the cumulative effect of mineral dissolution and oxidation. Bromate produced a more intense change in color of solutions at all pHs than chlorate, indicating it may be a more effective oxidant. We will present analytical results that provide experimental evidence of olivine alteration by oxyhalogen salts under Mars-like conditions.