Dear Ben,
From the perspective of someone who has already studied this in detail there are major un-overcomeable flaws in your hypothesis: Density/bouyancy of felsic vs mafic stock, shock melting dynamics, and lack of felsic minerals not already incorporated in existing continents.
Your theory does not take into account that the continents came in to existance very soon after differentation of the feldspars/silica( Felsic) and magnesium iron silicates( malfic) began circa 4.48± (?) bybp. Owing to their bouyancy differences, the felsic continents have remained floating on the heavier mantle mafic minerals ever since and this WILL always be that way. Continental mass is never subducted and owing to well understood plate tectonic dynamics, mountain building keeps pushing continental materials back up onto the continents themselves and felsic content gets recovered with great efficency.
You likely haven't done the math nor have you modeled it but I if you had you would not see a land mass antipodally but something of a pie-plate melengue of olivine glass derived from the mantle buldged up under an existing continent. We have an example of this on the asteroid Vesta but the scales for something like this happening on earth would be just shy of total core destruction. On vesta almost 1/3 of the asteroid was excavated and opposite that crater is a much less prominent, shallow sloped , buldge. Speaking of core, your impact energy transfer is never going to be one for one antipodally and the core is going to reflect, deflect and, absorb some of the energy. Likely less than 15% of that energy could ever be transfered antipodally even if the earthquake waves traveled with great efficency. A lot would be lost to friction within the planet. You are left with wave energy and not mass movement. High pressures on olivine yield a very compressd form called ringwoodite which is more likely to self absorb the over-pressure rather than produce a crustal blow out of physical mass --on the scale of the known impactors earth has collected anyway.
This hypothetical land form "buldge"--if it could it exist on earth would sink back down into the mantle because its mass density is higher than the surface density. Antipodal impact land formation could not account for any of our continental masses because their basement rocks are already well known to be felsic and bathtub shaped-- not cone shaped filled with malfic minerals. I mentioned source stock for these spash formed continents--that is felsic material lying around ouside an existing crustal system. There is no crustal mineral stock except already used in continental massed to give rise to impact generated continents.
On that basis I suggest you take this idea and see if it doesn't better apply to asteroidal settings. They physics of the earth and the size of the impactors needed but not found, pretty much shoot down this idea you spent so much reasoning on already-- but which you for whatever reason failed to consider the full rhelm of factors against it.
Traditionally when I post a rebuttal to someones pet project I get a range of but-but-buts or a personal attack or Hummph what do you know? yada yada. This time, owing to other obligations and failing vision I can't spend the time rehashing my opinion based on my experience and understanding--it is what it is and I am disinclined to write my own thesis-level reasons in rebuttal. My response was about principles and not through modeling stated values that show the physics in a definite mathmatical evaluation-true-- but I think the hypothesis can be nulled on the principle level alone. If you find a way to model this with realistic assumptions regarding impact energies and material behavior under such an impulse and want to bring that back for discussion then I'll try to get it another honest review (not that it will change existing contintental origin theory). Otherwise this is all I have to say on the topic. As written now, your tretise is but another incomplete theory mainly because your haven't handled all the real life factors that would support or affect your hypothesis --and they are major ones I don't think you can solve but it is your business if you want to pursue them.
One final bit of advice. You clearly have a deeply analytical brain that is dying to be unleashed. Don't unleash it fully until you have a good broad foundation in planetary geology. In this case, it truly is the stuff you don't know which can hurt you. Much of what I have talked about and much I didn't even go into such as the Ringwodite/Spinel zone would have been good to have knowledge of as you started writing.
Bottom Line: Antipodal dynamics do have a basis in planetary science but the continents were not formed by asteroidal collision transfered antipodally.
Regards,
Eman
Sorry my spell checker has stopped working but you bright people can figure it out.
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