¹Amanda Albright Olsen,²Elisabeth Hausrath,³J. Donald Rimstidt
¹School of Earth and Climate Sciences, University of Maine, Orono, ME, USA
²Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV, USA
³Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA

High salinity brines, although rare on Earth’s surface, may have been important in the geologic history of Mars. Increasing evidence suggests the importance of liquid brines in multiple locations on Mars. In order to interpret the effect of high ionic strength brines on olivine dissolution, which is widely present on Mars, forty-seven new batch reactor experiments combined with 35 results from a previous study conducted at 25°C from 1 < pH < 4 in magnesium sulfate, sodium sulfate, magnesium nitrate, and potassium nitrate solutions with ionic strengths as high as 12 m show that very high ionic strength brines have an inhibitory effect of forsterite dissolution rates. Multiple linear regression analysis of the data suggests that the inhibition in dissolution rates is due to decreased water activity at high ionic strengths. Regression models also show that mMg up to 4 m, and mSO4 up to 3 m have no effect on forsterite dissolution rates. The effect of decreasing dissolution rates with decreasing aH2O is consistent with the idea that water acts as a ligand that participates in the dissolution process. Less available water to participate in the dissolution reaction results in a slower dissolution rate. Multiple linear regression analysis of the data produces the rate equation inline image. Forsterite in dilute solutions with a water activity of one dissolve twice as fast as those in brines with a water activity of 0.8.

Reference
Olsen AA, Hausrath E, Rimstidt JD (2015) Forsterite dissolution rates in Mg-sulfate-rich Mars-analog brines, and implications the aqueous history of Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004664]

Published by arrangement with John Wiley&Sons