So, your "plate" that the ice wall sits on covers the whole of the underside of the earth too?
Do you not understand the legends? That is the crust, and the "plate" is part of the crust, just like the plates on a round Earth.
I can't comprehend your picture because it's utter dross. End of. Go back to school.
Then it's your problem that you can't comprehend pictures. Now, go back and revise plate tectonics. Actually, based on your reasoning, literacy, and comprehensive skills, I can only assume you're still a high school student. Get that high school geography textbook and read.