re: Simple Counter Questions
Olivine has also observed in exposed rocks in the walls -- well down the walls -- of Valles Marineris. Those deep layers have to be older than the plains surface above them, and those plains are fairly old. The chasms themselves are fairly old. So at least that package of basalt has been around a long time without chemical weathering.
I too am a non-geologist so I have no strong opinion, but the olivne exposed in what are unambiguously old rocks is one of the key pieces of evidence cited by the "white mars" camp.