re: How thick is the dust over cover?
"Anyone know how thick is the dust over cover of the glaciers?
There have been theories that might be relict glaciers left at near equatorial locations on Mars, but the consensus view is that they should have sublimated away even with a dust over cover. "
I think it's rock and dirt rather than dust.
As far as dust goes, a question might be what kinds rates of dust accumulation are there on Mars- a thin layer of dust on ice which is exposed to sunlight will cause it to "sublimated away", but if dust was say 1 cm or thicker it would be different situation.