Exhuming my thesis, part III

Update: added a footnote on the early history of plate tectonics at the end.

Following on Parts I & II here & here, here is an article on the breakup of Nuna Province in current N China: it gives new impetus to plate tectonics around 1.5GA - see Part II for another example -  such dynamic processes were proposed in my thesis paper here, where I applied more recent such dynamics to the Proterozoic of Southern Province of N Ontario Canada of similar age and make-up of Nuna Province. I looked at it from a structural geologic perspective, using intrusives cross-cutting relationships as date markers. The new paper actually dated similar intrusives in present day N China.

click to enlarge, original p.3 here

They suggest a vastly increased continental shelf environment:

"Our work reveals that deep Earth processes, specifically the breakup of the ancient supercontinent Nuna, set off a chain of events that reduced volcanic carbon dioxide emissions and expanded the shallow marine habitats where early eukaryotes evolved," said Professor Müller from the EarthByte Group at the University of Sydney.​

As Nuna fragmented, the total length of shallow continental shelves more than doubled to approximately 130,000 kilometers. These shallow-water environments likely hosted extensive oxygenated and temperate seas, providing stable, long-lived environments crucial for complex life to flourish.

I didn't go into such details, but the cross-section above proposed a large continental shelf setting:

 The thickness and facies variations reflect syndepositional down-to-the-basin (south) normal faulting that controlled the accumulation and preservation of the lower three Huronian megacycles. These are overlapped northward by the youngest megacycle, an extensive sheet of clastic sediments recording post-stretching regional subsidenceof the cratonic margin due to cooling and thermal contraction. Soft-sediment folds in the rocks of the youngest megaycycle to the extreme south probably indicate southward slumping into an adjacent basin. Nipissing diabase instrusions, 2100 Ma old, cut Huronian strata and soft-sediment folds...

It's more in the clastic environment, the areal extent hard to quantify because of the metamorphic grade compression. But the map & scale above the cross-section gives an appreciation for the less-disturbed section's extent N of the Murray Fault Zone. Later discussions ranged into glaciation and clastic environs, so little is said about the onset of life as discussed in the other paper. Darrel Long summarized more discussions here halfway between my thesis and now, and Paul Hoffman here shortly after my thesis.

Early history of plate tectonics 

My thesis in the early eighties was amidst the confirmation and widespread use of what was then still called a theory. The University of Calgary hosted visiting professors John Dewey & Kevin Burke, alumni of Warren Carey who influenced my thesis supervisor Ray Price - see his Penrose Medal lecture here - an environment that allowed me to push such ideas into the Precambrian: that contrasts with the early history of plate tectonics; this somewhat belabored video, here re: the history of science, lays the foundation of all that. Many will recognize toward the end the work of Harry Hess and Mary Tharpe, popularized by the 1968 National Geographic map of the Mid-Atlantic ridge here.