Lebrón-Rivera, Sully A.

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    Experimental hydration of amorphous silicate smokes: Simulating aqueous alteration of fine-grained materials in CM chondritic meteorites
    (2017) Lebrón-Rivera, Sully A.; Chizmadia, Lysa; College of Arts and Sciences - Sciences; Gilbes, Fernando; Hudgins, Thomas; Department of Geology; Perales, Oscar
    Amorphous non-stoichiometric silicate materials (e.g. “smokes”) of different compositions (e.g. SiOx, Mg-SiOx, Fe-SiOx, and Mg-Fe-SiOx) synthesized at NASA’s Goddard Space Flight Center are used as analogs for the amorphous materials found in the matrices of the most primitive meteorites (e.g CM’s, CO’s, and CR’s). Because the CM chondrites were aqueously altered at ~22-25 ºC, a series of hydration experiments were performed at room temperature to see how the succession of hydrous minerals proceeds with time. pH-time series and temperature-time series data were measured as an attempt to characterize the reactions that occur during the aqueous alteration of non-stoichiometric silicates. In addition, hydration of the Fe-SiOx smoke using Mg solutions at different concentrations were performed to assess the role of dissolved ions during aqueous alteration of primitive CM chondrites. The hydration of Mg-silicate smokes results in alkaline values with an average pH of 10.93 (± 0.21). Alkaline values are consistent with serpentinizing reactions such as those seen in CM chondrites and help explain the preservation of Fe-Ni metal grains while the acidic values obtained by the hydration of the Fe-SiOx (as low as 4.26 (± 0.37)) does not. Hydration of Mg-silicate and Fe-silicate smokes mechanical mixtures also result in alkaline values. Higher Fe contents result in less alkaline values, therefore, the pH obtained by the higher Mg:Fe ratios are more consistent with CM chondrites. Hydration of the Fe-SiOx smokes using MgO solution resulted in an alkalinity with an average pH of 9.75 (± 0.42) at high concentrations, and using Mg(Cl)2 solutions result in acidic values of 5.01 (± 0.44) at high concentrations. Only the MgO solution at high concentrations resulted the pH necessary to reproduce the textures seen in CM chondrites. Temperature changes in the reactions are less than 1 degree, which is consistent with observations that CM chondrites were altered at low temperatures. This helps explain the preservation of low temperature phases, which is most consistent with the alteration of the anhydrous amorphous material rather than the anhydrous silicates. SEM characterization reveals individual particles ranging from 50-200 nm in size. The smoke:water experiments shows a slight change in texture from individual particles to closely- packed/fused textures after a period of 3 months of reaction. The Fe smoke:solution experiments still preserved the initial particulate nature and no secondary minerals could be identified.