Supercontinent

In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leaves room for interpretation and is easier to apply to Precambrian times. To separate supercontinents from other groupings, a limit has been proposed in which a continent must include at least about 75% of the continental crust then in existence in order to qualify as a supercontinent.
Moving under the forces of plate tectonics, supercontinents have assembled and dispersed multiple times in the geologic past. According to modern definitions, a supercontinent does not exist today; the closest is the current Afro-Eurasian landmass, which covers approximately 57% of Earth's total land area. The last period in which the continental landmasses were near to one another was 336 to 175 million years ago, forming the supercontinent Pangaea. The positions of continents have been accurately determined back to the early Jurassic, shortly before the breakup of Pangaea. Pangaea's predecessor Gondwana is not considered a supercontinent under the first definition since the landmasses of Baltica, Laurentia and Siberia were separate at the time.
A future supercontinent, termed Pangaea Proxima, is hypothesized to form within the next 250 million years.

Theories

The Phanerozoic supercontinent Pangaea began to break up and this distancing continues today. Because Pangaea is the most recent of Earth's supercontinents, it is the best known and understood. Contributing to Pangaea's popularity in the classroom, its reconstruction is almost as simple as fitting together the present continents bordering the Atlantic ocean like puzzle pieces.
For the period before Pangaea, there are two contrasting models for supercontinent evolution through geological time.

Series

The first model theorizes that at least two separate supercontinents existed comprising Vaalbara and Kenorland, with Kenorland comprising Superia and Sclavia. These parts of Neoarchean age broke off at ~2480 and, and portions of them later collided to form Nuna. Nuna continued to develop during the Mesoproterozoic, primarily by lateral accretion of juvenile arcs, and in Nuna collided with other land masses, forming Rodinia. Between ~825 and Rodinia broke apart. However, before completely breaking up, some fragments of Rodinia had already come together to form Gondwana by. Pangaea formed through the collision of Gondwana, Laurasia, and Siberia.

Protopangea–Paleopangea

The second model is based on both palaeomagnetic and geological evidence and proposes that the continental crust comprised a single supercontinent from until break-up during the Ediacaran period after. The reconstruction is derived from the observation that palaeomagnetic poles converge to quasi-static positions for long intervals between ~2.72–2.115 Ga; 1.35–1.13 Ga; and with only small peripheral modifications to the reconstruction. During the intervening periods, the poles conform to a unified apparent polar wander path.
Although it contrasts the first model, the first phase essentially incorporates Vaalbara and Kenorland of the first model. The explanation for the prolonged duration of the Protopangea–Paleopangea supercontinent appears to be that lid tectonics prevailed during Precambrian times. According to this theory, plate tectonics as seen on the contemporary Earth became dominant only during the latter part of geological times. This approach was widely criticized by many researchers as it uses incorrect application of paleomagnetic data.

Cycles

A supercontinent cycle is the break-up of one supercontinent and the development of another, which takes place on a global scale. Supercontinent cycles are not the same as the Wilson cycle, which is the opening and closing of an individual oceanic basin. The Wilson cycle rarely synchronizes with the timing of a supercontinent cycle. However, supercontinent cycles and Wilson cycles were both involved in the creation of Pangaea and Rodinia.
Secular trends such as carbonatites, granulites, eclogites, and greenstone belt deformation events are all possible indicators of Precambrian supercontinent cyclicity, although the Protopangea–Paleopangea solution implies that Phanerozoic style of supercontinent cycles did not operate during these times. Also, there are instances where these secular trends have a weak, uneven, or absent imprint on the supercontinent cycle; secular methods for supercontinent reconstruction will produce results that have only one explanation, and each explanation for a trend must fit in with the rest.
The following table names reconstructed ancient supercontinents, using Bradley's 2011 looser definition, with an approximate timescale of millions of years ago.

Supercontinent name	Age	Period/Era Range	Comment
Vaalbara	3,636–2,803	Eoarchean-Mesoarchean	Also described as a supercraton or just a continent
Ur	2,803–2,408	Mesoarchean-Siderian	Described as both a continent and a supercontinent
Kenorland	2,720–2,114	Neoarchean-Rhyacian	Alternatively the continents may have formed into two groupings Superia and Sclavia
Arctica	2,114–1,995	Rhyacian-Orosirian	Not generally regarded as a supercontinent, depending on definition
Atlantica	1,991–1,124	Orosirian-Stenian	Not generally regarded as a supercontinent, depending on definition
Columbia	1,820–1,350	Orosirian-Ectasian
Rodinia	1,130–750	Stenian-Tonian
Pannotia	633–573	Ediacaran
Gondwana	550–175	Ediacaran-Jurassic	From the Carboniferous, formed part of Pangaea, not always regarded as a supercontinent
Pangaea	336–175	Carboniferous-Jurassic

Volcanism

The causes of supercontinent assembly and dispersal are thought to be driven by convection processes in Earth's mantle. Approximately 660 km into the mantle, a discontinuity occurs, affecting the surface crust through processes involving plumes and superplumes. When a slab of the subducted crust is denser than the surrounding mantle, it sinks to discontinuity. Once the slabs build up, they will sink through to the lower mantle in what is known as a "slab avalanche". This displacement at the discontinuity will cause the lower mantle to compensate and rise elsewhere. The rising mantle can form a plume or superplume.
Besides having compositional effects on the upper mantle by replenishing the large-ion lithophile elements, volcanism affects plate movement. The plates will be moved towards a geoidal low perhaps where the slab avalanche occurred and pushed away from the geoidal high that can be caused by the plumes or superplumes. This causes the continents to push together to form supercontinents and was evidently the process that operated to cause the early continental crust to aggregate into Protopangea.
Dispersal of supercontinents is caused by the accumulation of heat underneath the crust due to the rising of very large convection cells or plumes, and a massive heat release resulted in the final break-up of Paleopangea. Accretion occurs over geoidal lows that can be caused by avalanche slabs or the downgoing limbs of convection cells. Evidence of the accretion and dispersion of supercontinents is seen in the geological rock record.
The influence of known volcanic eruptions does not compare to that of flood basalts. The timing of flood basalts has corresponded with a large-scale continental break-up. However, due to a lack of data on the time required to produce flood basalts, the climatic impact is difficult to quantify. The timing of a single lava flow is also undetermined. These are important factors on how flood basalts influenced paleoclimate.

Plate tectonics

Global palaeogeography and plate interactions as far back as Pangaea are relatively well understood today. However, the evidence becomes more sparse further back in geologic history. Marine magnetic anomalies, passive margin match-ups, geologic interpretation of orogenic belts, paleomagnetism, paleobiogeography of fossils, and distribution of climatically sensitive strata are all methods to obtain evidence for continent locality and indicators of the environment throughout time.
Phanerozoic and Precambrian had primarily passive margins and detrital zircons, whereas the tenure of Pangaea contained few. Matching edges of continents are where passive margins form. The edges of these continents may rift. At this point, seafloor spreading becomes the driving force. Passive margins are therefore born during the break-up of supercontinents and die during supercontinent assembly. Pangaea's supercontinent cycle is a good example of the efficiency of using the presence or lack of these entities to record the development, tenure, and break-up of supercontinents. There is a sharp decrease in passive margins between 500 and during the timing of Pangaea's assembly. The tenure of Pangaea is marked by a low number of passive margins during 336 to and its break-up is indicated accurately by an increase in passive margins.
Orogenic belts can form during the assembly of continents and supercontinents. The orogenic belts present on continental blocks are classified into three different categories and have implications for interpreting geologic bodies. Intercratonic orogenic belts are characteristic of ocean basin closure. Clear indicators of intracratonic activity contain ophiolites and other oceanic materials that are present in the suture zone. Intracratonic orogenic belts occur as thrust belts and do not contain any oceanic material. However, the absence of ophiolites is not strong evidence for intracratonic belts, because the oceanic material can be squeezed out and eroded away in an intracratonic environment. The third kind of orogenic belt is a confined orogenic belt which is the closure of small basins. The assembly of a supercontinent would have to show intracratonic orogenic belts. However, interpretation of orogenic belts can be difficult.
The collision of Gondwana and Laurasia occurred in the late Palaeozoic. By this collision, the Variscan mountain range was created, along the equator. This 6000-km-long mountain range is usually referred to in two parts: the Hercynian mountain range of the late Carboniferous makes up the eastern part, and the western part is the Appalachian Mountains, uplifted in the early Permian. The locality of the Variscan range made it influential to both the northern and southern hemispheres. The elevation of the Appalachians would greatly influence global atmospheric circulation.