It's very easy to play this game with gravity and elevation maps and to find quasi-circular features hundreds of km across. the vast majority of them have the wrong balance of gravity anomaly and elevation or have no geological evidence of a major impact.

In many cases, we just don't know what is the specific cause of the QCD, but we can rule out an impact. When the target area is buried under a continental icecap, then ground truth is rather harder to obtain and these features all look very tempting. But go back to the elevation map that Vince posted - see just how many "big circles" you can fit in there.

I can show you a half-dozen convincing examples in the southeast of Australia - also a Gondwanaland terrane.

The Russians used to do a lot of this type of analysis and none of their mega-scale QCD's ever passed geological muster.

This idea should be placed in the box labelled "Interesting but unproven" and further research invited. It may be premature to rush out to Wilkes' Land and start drilling for core samples, but certainly some further work is called for.