Wilson's supercontinent cycles

[Florian]

I made a figure to further illustrate why Wilson cycles are actually artifactual:

Wilson-cycles.png (121.39 KiB) Viewed 5221 times

Every letter identifies a terrane that formed at a specific time. Let's say that the age of the different terranes is:

A: 400 Ma
B: 700 Ma
C: 100 Ma
D: 1000 Ma
E: 1300 Ma

The different parts are now dispersed on different continents but their age can help to make a reconstruction of the globe history.

We note that if the globe radius has remained fixed, we must break up the present continents and then rebuild new one to reform terrane A, and then break up the continents again and so on, to reconstruct the full history of these terranes. This is Wilson's cycle of supercontinents.

But there is another solution which does not require to break up the continents and yet allows to explain the current dispersal of the terranes. This solution is to simply reduce the size of the globe.

When multiple independent problems can be solved by the same solution, then this is probably the right solution, even if it seems a priori implausible.

[sathearn]

Thanks for this useful aid to visualization.

Of course one may reassemble these terranes for any of the given time intervals by breaking up the present continents. However, I don't see that one must "break up" the present continents (presumably the three continents in your graphic represent the "present" continents and their arrangement on the globe) in order to reassemble terrane A (or any of the others) at a former time. What will happen in any such reassembly (if the integrity of the continents is maintained), is that other regions (portions of the other terranes) which share clear affinities during any other time interval but that of the reassembly will be widely separated from their conjugates.

Either way, wide gaps are created between allied terrane elements, and so you do get openings and closings of wide, though possibly artefactual oceans.

It must be granted that the Wilson Cycles as originally proposed are partially inferred from floral and faunal differences among contemporaneous terranes that are now juxtaposed - for example, higher endemism among some relevant terranes in the Early Devonian might indicate their separation by persistent marine barriers (wide oceans, in common reconstructions).

But there are also inferences that more closely resemble your graphic. For example, in the Rodinia reconstructions, "East Gondwana" (i.e. Australia/Antarctica ) was joined with the western Americas. At the same time, "West Gondwana" consisted principally of united South America/Africa. On a globe of present radius, this configuration implies the existence of a very wide ocean (~10,000 km) between East Gondwana and West Gondwana (i.e. eastern Africa). On the same assumption, further inferences about the time frame for closure of this ocean - ~100 Ma or more - are suggested. Given paleomagnetic evidence dating the beginning of divergence between Laurentia (North America) and East Gondwana (Australia, primarily) at between 720 and 700 Ma, East Gondwana/West Gondwana collision is suggested to have begun no earlier than 625 -600 Ma. (See J. G. Meert, (1999) "Some perspectives on the assembly of Gondwana," in T. Radhakrishna and J.D. Piper, eds., The Indian Subcontinent and Gondwana: A Palaeomagnetic and Rock Magnetic Perspective, Geological Society of India, Memoir 44 pp. 45-58,. Meert is admirably explicit about the involvement of the present-radius assumption in these inferences.)

[Florian]

Thanks for this useful aid to visualization.

Of course one may reassemble these terranes for any of the given time intervals by breaking up the present continents. However, I don't see that one must "break up" the present continents (presumably the three continents in your graphic represent the "present" continents and their arrangement on the globe) in order to reassemble terrane A (or any of the others) at a former time. What will happen in any such reassembly (if the integrity of the continents is maintained), is that other regions (portions of the other terranes) which share clear affinities during any other time interval but that of the reassembly will be widely separated from their conjugates.

That's right! One must not necessarily break up the continents in these conditions.

Let's try to give a better example.
What if the age of the terranes was:
A and B : 400 Ma
C, D and E: 800 Ma

I think that would require continental breakage, right?