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Phyllosilicate Formation on Early Mars Via Open-System Acid Alteration of Basaltic GlassSmectites are widespread on Mars, but neutral/alkaline conditions favorable for smectite formation have surprisingly not led to abundant carbonates. Smectite formation on Mars could also occur in acidic environments unfavorable for carbonate formation. Acidic smectite formation has been demonstrated in batch (closed hydrologic) systems, however, the mechanisms and octahedral composition of smectite forming in acidic flow-through (open hydrologic) systems are not fully understood. Stapafell basaltic glass was hydrothermally altered (190◦C) at two flow rates corresponding to low and high water to rock ratio (W/R) and initial pH (pH_0) values of 2, 3, 4 and 6, and a batch low W/R experiment was conducted at pH_0 2. Kaolinite, montmorillonite and chlorite formed at pH_0 2 at low W/R; no phyllosilicates formed at pH_0 2 at high W/R; and lizardite formed at pH_0 ≥3 at both W/R ratios. Lizardite, kaolinite, and montmorillonite in these experiments formed by precipitation from solution and chlorite likely formed through alteration of montmorillonite and/or basalt. Saponite formed at pH_0 2 in batch conditions by alteration of basaltic glass. Comparison of experimental data with martian phyllosilicate assemblages indicated that smectite formation on Mars likely occurred under water-limited conditions. Al-rich smectite could form in open-system low W/R subsurface environments under a narrow range of pH (pH <3) while saponite could form in closed low W/R systems under acidic to alkaline conditions. Combined open and closed hydrological regimes could be responsible for development of clay mineral stratigraphies observed on Mars. The acidic conditions required for formation of Al-rich smectite were unfavorable for carbonate precipitation, but carbonate precipitation could occur together with Fe/Mg-smectite in closed systems at pH >4. The lack of carbonates occurring together with Fe/Mg-smectite could be cause by low pCO2 in subsurface closed environments and/or by overall lack of carbonate precipitation despite significant oversaturation.
Document ID
20230010746
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
S J Ralston
(Jacobs (United States) Dallas, Texas, United States)
Tanya Peretyazhko
(Jacobs (United States) Dallas, Texas, United States)
Brad Sutter
(Jacobs (United States) Dallas, Texas, United States)
Douglas W Ming
(Johnson Space Center Houston, Texas, United States)
Richard V Morris
(Johnson Space Center Houston, Texas, United States)
Angela Garcia
(Jacobs (United States) Dallas, Texas, United States)
Amanda Marie Ostwald
(University of Nevada, Las Vegas Las Vegas, Nevada, United States)
Date Acquired
July 24, 2023
Subject Category
Geosciences (General)
Lunar and Planetary Science and Exploration
Meeting Information
Meeting: ASA-CSSA-SSSA International Annual Meeting
Location: St. Louis, MO
Country: US
Start Date: October 29, 2023
End Date: November 1, 2023
Sponsors: Crop Science Society of America, American Society of Agronomy, Soil Science Society of America
Funding Number(s)
WBS: 857464.05.05
Distribution Limits
Public
Copyright
Portions of document may include copyright protected material.

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