It could be possible that the Borealis basin was formed when the Martian tectonic plates ceased to move when it had a super continent like Pangea except it occupied a greater percentage of Mars.
The Boreal Basin on Mars was a Martian version of a large Martian oceanic plate Whereas the southern twothirds were a supercontinent caused by Martian continental plates grouped together.

After the Martian tectonic plates ceased moving erosion flattened out the boundary at present day Arabia Terra and Amazonis Planitia.
Then The impacts that created the
Hellas,Argyre, and Isidis basins caused further volcanism at Tharsis,Elysium, and Syrtis respectively

The Thaumasia plataeu is one of those plates and topographic maps from all the martian spacecraft show that it was later temperarly reanimated by the Tharsis volcanoes which the resulting stress on the Martian crust caused it to move south and caused mountains and some volcanoes to form akin to the Earths cascade range while opening the Valles Marineris and a change in direction of movement by the Argyre impact caused blocks of the plate to be seperated at the Noctis Labyrinthus from the sudden short jolt towards Tharsis from the impact.

I belive that Mars actually have never had active tectonism, able to create (and break apart) supercontinents. One proof of this may be the height of Tharsis volcanoes, created by hot-spot plumes (like Hawaii here on Earth), but with a fixed crust, magma kept on erupting (for milions of years?) always in the same place, creating these gigantic volcanoes. if there were some tectonism, there would be a chain of volcanoes istead.
(of course tharsis volcanism can be hundreds of milions of year younger than the last plate motion......if ever been one)

Here is a great paper explaining some of the theories about the formation of Vastitas Borealis
http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.earth.35.031306.140220

What i meant was that the possible Thaumasia plate was reanimated by the weight of the forming Tharsis complex.
This resume of southeast plate motion probably only lasted 2 to 5 maybe even 10 million years.
And the formation of the Argyre basin by impact changed its plate motion to the west then the still growing Tharsis complex changed the movement back to the southeast for a short time, after that the Thaumasia plate became like the rest of the tectonic plates on Mars, motionless never to move again.
The Thaumasia plate theory could explain why the Syria Planum low shield volcanoes and lava flows get younger toward the northeast of the Syria Planum volcano complex.
this age trend must have be caused by the Thaumasia plate moving over a small hotspot.