Exhuming my thesis, part III

Update 1: follow-on post here on the series revisiting maps or posting off-web.

Update 2: added an intriguing speculation on the adjacent Sudbury Nickel Irruptive

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 over 40 yrs. ago here, where I applied recent plate 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.

Subbury Nickel Irruptive

A related article summarized the knowledge & setting of this intriguing structure adjacent to the Southern Province, more later. This map shows a "Huronian outlier" that underscores the minimum extent of the clastic shelf ~ 1.9Ga, not unlike the extensive platforms mentioned in the Nuna Province of China.

Click to enlarge, original article here

But wait! The 3I/Atlas interstellar comet  currently streaking the solar system offered an intriguing speculation - not that any more were needed! - Anton Petrov's excellent video here mentioned in passing a high Nickel content among many notable facts. This prompted my following comment that was pinned here:

Aha! Higher levels of Ni... the Sudbury Nickel Irruptive in N Ontario, Canada might've been struck by an interstellar comet ~1.9B yrs ago? 

('Irruptive' is a compromise word ~ arguments abt ejecta being from Precambrian mega volcanism or a cometary impact)

The current concensus is the impact theory: the ellipsoid shape would reflect an angular strike, and the oval would have been then changed by subsequent tectonism; the flat eastern end for ex. reflects the Grenville Front smashing into it later.