[cripplecreek]

I was reading that one of the theories about mars is that a major impact disrupted the convection currents and halted any plate tectonics that may have been going on there.

[JRandomFreeper]

If you can follow it, Margarita Marinova (before her PhD) did a presentation on the Martian Dichotomy. It adds a lot of information to what you are talking about.

You can find that talk by mashing: here.

/johnny