This is Part-1 of our Plate Tectonics history series. We will start with Supercontinent Rodinia, a name derived from Russian word Rodit which means to give birth or Rodina which means motherland.
Rodinia was a Neoproterozoic (1,000 to 541 million years ago) supercontinent that accumulated 1.1–0.9 billion years ago and split 750–633 million years ago.
It was first named Pangea I in the 1870s. McMenamin & McMenamin renamed it Rodinia in 1990, who were the first to produce a reconstruction and offer a supercontinent temporal framework.
Summary
Rodinia developed at c. 1.23 Ga by collision and accretion of fragments produced by the breakup of an older supercontinent, Columbia, joined by global-scale 2.0–1.8 Ga collisional episodes.
Rodinia crashed the Neoproterozoic with its continental remains reassembled to develop Pannotia 633–573 million years ago. However, unlike Pannotia, little is known yet about the exact geodynamics and configuration history of Rodinia. Paleomagnetic evidence provides clues to the paleolatitude of different parts of the Earth’s crust, but not to their longitude, which geologists have pieced together by linking similar geologic features, often now generally dispersed.
The excessive cooling of the global climate around 717–635 million years ago (the so-called Snowball Earth of the Cryogenian period) and the accelerated evolution of old life during the following Cambrian and Ediacaran periods are thought to have been triggered by the breaking up of Rodinia or to a slowing down of tectonic processes.
Geodynamics
The notion that a supercontinent existed in the early Neoproterozoic began in the 1970s when geologists discovered that orogens of this age exist on virtually all cratons. Examples are the Grenville orogeny in Dalslandian orogeny in Europe and North America.
Since then, many alternative restorations have been introduced for the shape of the cratons in this supercontinent. Most of these reconstructions are based on the relationship of the orogens on several cratons. Though the shape of the core cratons in Rodinia is now reasonably well known, new reconstructions still differ in many details. Geologists try to decrease the uncertainties by collecting palaeomagnetic and geological data.
Most reconstructions show Rodinia’s center formed by the North American craton, circled in the southeast with the East European craton, the Amazonian craton, and the West African craton; in the south with the São Francisco and Río de la Plata cratons; in the southwest with the Congo and Kalahari cratons; and in the northeast with India, Australia and eastern Antarctica. The positions of North and South China and Siberia north of the North American craton differ enormously depending on the reconstruction.
Break up
Rodinia broke up in 4 stages between 825–550 Ma.
A superplume initiated the break up around 825–800 Ma whose influence—such as intense bimodal magmatism, crustal arching, and collection of thick rift-type sedimentary successions—have been recorded in India, South Australia, Tarim, South China, Arabian-Nubian Craton, and Kalahari.
Rifting advanced in the same cratons 800–750 Ma and expanded into Siberia and perhaps Laurentia. India and the Congo-Säo Francisco Craton were either separated from Rodinia during this period or never were part of the supercontinent.
As the middle part of Rodinia reached the Equator around 750–700 Ma, a new pulse of rifting and magmatism continued the disassembly in West Australia, western Kalahari, South China, and Tarim margins of Laurentia.
Between 650–550 Ma, several events coincided: the closure of the Braziliano, the opening of the Iapetus Ocean, closure of Mozambique, and Adamastor oceans; and the Pan-African orogeny. The result was the creation of Gondwana land.
Influence on paleoclimate and life
Unlike more modern supercontinents, Rodinia would have been completely barren. Rodinia survived before complex life populated dry land. Based on sedimentary rock analysis, Rodinia’s development happened when the ozone layer was not as widespread as today. Ultraviolet light checked organisms from inhabiting its interior. Nevertheless, its presence did significantly impact the marine life of its time.
In the Cryogenian period, the Earth experienced massive glaciations, and temperatures were as cold as today. Large areas of Rodinia may have been covered by southern polar ice cap and glaciers.
Low temperatures may have been distorted during the initial stages of continental rifting. Geothermal heating tops in crust about to be rifted, and since warmer rocks are less dense, the crustal rocks rise relative to their neighborhood. These rising forms areas of higher altitude, where the air is ice and cooler, are less likely to melt with season changes. It may explain the proof of large scale glaciation in the Ediacaran period.
