"However, even rare events of liquid water formation would be significant since they would dominate the chemistry of the soil"
The OMEGA/CRISM measurements demonstrate emphatically that the soil and dust of Mars is dominated by dry and cold chemical processes and NOT liquid water interactions since the end of the Hesperian era some 3.5 billion years ago.
Ergo, melting does not occur in any significant range of space and time and HAS NOT DONE SO for the past 3.8 BILLION years.
What part of this do you not get?