I wrote this and somehow missed Percy's reply which addresses the same point I had but rather than just toss out my post I thought I would just put it up just to reiterate what Percy is saying.
---Original Post---------------------------------
Nobody has addressed these issues and they are VERY softball in nature so I thought I would intrude. rox or someone with actual credentals can certainly correct any errors I made.
1. You will note on the map that ocean crust is `bumping' into quite a bit of continental mass, especially along the Atlantic, Indian Ocean, Arctic, etc., and.. get off the phone because there's no subduction zone! What's up doc? We've got lots of youthful ocean crust bumping up against a bunch of geriatric rock!
2. You will also notice that S. America and Africa are getting squeezed' by MOM's on both sides. Watch out... those continents just might pop out!
The one BIG assumption that you are making that would even allow you to think that either of these statements makes any sense is that the plate boundaries are always at the edge of where continental crust meets oceanic crust. This is totally not true.
Look at this map of the plates.
Wikimedia Error
Look in particular at North America. It is not being "squeezed" at all because the continent and the half of the Atlantic sea floor west of the mid Atlantic ridge are all part of the SAME PLATE.
The "missing" subduction zone you are looking for is on the west end of that plate on the west coast of North America.
It appears that you have a FUNDAMENTAL misunderstanding of what plate tectonic theory even is if you have such a bad misconception such as that all continental crust and ocean crust are on seperate plates.
If a nation expects to be ignorant and free, in a state of civilization, it expects what never was and never will be. --Thomas Jefferson
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