But, to conjecture that plate tectonics stopped, I disagree. There was an extensive intrusive event across western North America at 1.4 Ga that emplaced many plutons. In Colorado they are called the Silver Plume Granites. Interesting rocks. Water rich, many pegmatites. Then there is the Pikes Peak Granite at ~1 Ga. Now it is considered to be anorogenic, not associated with subduction, and still a bit of an odd occurrence. But we know that it did feed a volcanic edifice on the surface because volcanic rocks of the same age and chemistry are found in wells under the Great Plains.

The article properly points out that mountain building and erosion are a balance. My thought is that while mountain building along continental margins was reduced during this period due to the mega continent, the processes were still active, just overwhelmed by erosion.

This latest paper supports earlier research showing that the oceans of the time were nutrient starved.

Thanks for the link.