Award Date

12-1-2015

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Elisabeth M. Hausrath

Second Committee Member

Oliver Tschauner

Third Committee Member

Megan Elwood Madden

Fourth Committee Member

Brian Hedlund

Number of Pages

90

Abstract

Water is essential to life on Earth and is likely to play a role in determining the habitability of other planets. Pure liquid water is not stable on the surface of Mars but brines can temporarily remain liquid, and increasing evidence suggests the presence of recent liquid water, including brines, on Mars. Brines can host life at temperatures as low as -30 ºC and some organisms can live at activities of water as low as 0.61. Therefore, if brines have been present on Mars, they may act as habitable environments.

The Fe-rich smectite nontronite, (CaO0.5,Na)0.3 Fe3+2(Si,Al)4O10(OH)2·nH2O, has been detected on the surface of Mars, particularly in ancient terrains. If the surface of Mars experienced brine solutions throughout its history, those brines have likely impacted nontronite. Therefore, understanding alteration of nontronite in brines can help interpret past aqueous, and potentially habitable, conditions on Mars.

To interpret interactions of nontronite with brines, duplicate batch experiments were used to measure the dissolution rates of nontronite at 25 ºC at activities of water (aH2O) of 1.00 (0.01 M CaCl2 or NaCl representative of dilute waters), 0.75 (saturated NaCl and 3.00 mol kg-1 CaCl2), and 0.50 (5.00 mol kg-1 CaCl2). Experiments at aH2O = 1 (0.01 M CaCl2) were also conducted at 4 ºC, 25 ºC, and 45 ºC to calculate an apparent activation energy for dissolution of nontronite.

Results indicate that with decreasing activity of water the dissolution rate of nontronite also decreases. Dissolution rates at 25 ºC in CaCl2-containing solutions decreased with decreasing activity of water as follows: 1.18x10-12 ± 9.30 x10-14 moles mineral m-2 s-1(aH2O = 1)> 2.36x10-13 ± 3.07 x10-14 moles mineral m-2 s-1( aH2O = 0.75)> 2.05x10-14 ± 2.87 x10-15 moles mineral m-2 s-1 ( aH2O = 0.50). Similar results were observed at 25 ºC in NaCl-containing solutions with dissolution rates as follows: 1.89x10-12 ± 9.59 x10-14 moles mineral m-2 s-1 (aH2O = 1)> 1.98x10-13 ± 2.26x10-14 moles mineral m-2 s-1(aH2O = 0.75). An apparent activation energy of 54.6 ± 1.0 kJ/mol was calculated from the following dissolution rates in dilute CaCl2- containing solutions at temperatures of 4 ºC, 25 ºC, and 45 ºC: 2.33x10-13 ± 1.25x10-14 moles mineral m-2 s-1( 4 ºC), 1.18x10-12 ± 9.30 x10-14 moles mineral m-2 s-1( 25 ºC), and 4.98x10-12 ± 3.84 x10-13 moles mineral m-2 s-1( 45 ºC).

These results suggest that martian nontronite perceptibly altered by brines at low temperatures may have experienced very long periods of water-rock interaction, with important implications for the paleoclimate and long-term potential habitability of Mars.

Keywords

Brines; Clay Minerals; Dissolution Kinetics; Mars; Planetary Geochemistry; Planet exploration

Disciplines

Geochemistry | Geology

Language

English


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