Recently the Mesoproterozoic Era has been divided into the following Periods (with arbitrarily defined boundaries): Calymmian ("covering", after the development of platforms: 1.60 - 1.40 Ga), Ectasian ("extension", both of platforms and of the beginnings of the rifting events: 1.40 - 1.20 Ga), and Stennian ("narrowing", after narrow belts of intense metamorphism and deformation, such as the Grenville Orogeny: 1.20 - 1.00 Ga).

Mesoproterozoic saw high amounts of igneous activity. It may be due to large-scale mantle "superplumes" forming underneath the first continental or supercontinental (not yet observed) granitic masses.

• Keweenawan (failed) Rift:
  • Mid-continental rift through middle of Laurentia, about 1.2-1.0 Ga
  • Had potential to split Laurentia in two, but did not finish the job
• Giant basaltic flows (flood basalts) around 1.3 Ga.
• Dike "swarms" throughout much of Laurentia, and elsewhere, at this time (1.267 Ga); was an earlier similar event at 2.45 Ga).

Belt Supergroup: a huge (16 km thick!) sequence of terrestrial mudstones, shallow marine sandstones & limestones & turbidites in western North America, deposited from 1.45 to 0.85 Ga. A huge filled-in down-warped basin of western Laurentia.

During late Mesoproterozoic, assembly of the first well-known supercontinent Rodinia (newer reconstruction; requires online access to Lyell collection):

• Grenville Orogeny:
  • Down eastern ridge of Laurentian craton, represents continent-continent collision, c. 1.3-1.0 Ga
• Laurentia apparently near center of Rodinia: other cratons assembled around it.
• The Grenville Orogen + the pre-orogeny Laurentian craton represent 75% of North America + Greenland; everything else added during Phanerozoic.

[Someone has created the Rodinian National Anthem: note, music starts automatically when you launch the page.]

During Neoproterozoic, Rodinia rifts apart around 750 Ma: birth of Pacific Ocean (although generally we call it the Panthalassic Ocean until the break up of Pangaea in the Mesozoic).

From this point onward, western Laurentia never has contact with continental-size masses (although much of the far western part of North America was accreted during the Phanerozoic).

The Pan-African Orogeny (and related orogenies):

• Latest Neoproterozoic collision of the previously unassociated cratons that make up Africa
• New dating suggests assembly by 600 Ma
• Represents assembly of another supercontinent: Pannotia (Newer reconstruction; requires access to Lyell collection)

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Last modified: 19 January 2012