geologic plates of Earth mapped; etc.

 https://logiclogiclogic.wordpress.com/2016/02/18/another-big-failure-in-climate-science-underwater-volcanoes/

-back 80 million years

The Pacific Antarctic Ridge may be the least-studied of the underwater volcanic mountains that crisscross the globe. Blue square indicates suspected vents. Credit: Modified image from Chris German and Karen Von Damm  
https://phys.org/news/2010-03-scientists-apparent-hydrothermal-vents-antarctica.html#jCp
..........

 https://earthhow.com/antarctic-plate/

https://worldbuilding.stackexchange.com/questions/65246/the-arctic-plate