My suspicion is a large space monster, some massive killer from the void ran into mars at one point. The point opposite is where the resulting quake waves converge tearing apart the crust, liquefying the mantle, encouraging a volcano complex.

Also, whatever caused the Noctis Labyrinthus (west side of the valley in the article south east of the volcanoes) is a wild geologic process I don't think I have seen anywhere else. The large valley looks sort of like a rift valley, and erosion canyons are obvious, but Noctis Labyrinthus with it's fragmented plate look is weird, my best guess is a rift valley where three plates are separating, but that is a weak guess.