Gee, TC, why don't you check out
this crater list for a list of [currently] discovered impact craters. If you want to find out more about them individually, try going to google, advanced search, and typing in the name. If your "caldera theory" is correct, evidence should be visible at all or at least most. Oddly, the only thing anyone's found relative to these formations is shocked quartz and other impact indicators. Must be that divine deception in action again.
You do realize that Walter Brown's geology - which is where this idea originated, although I'm not sure specifically where you got it - has been quite thoroughly refuted by mainstream geologists?