Orthoversion and Introversion Models of Supercontinent Formation

The Orthoversion and Introversion models are two leading hypotheses proposed to explain the cyclic formation and breakup of supercontinents throughout Earth’s geological history. These models describe how fragments of former supercontinents reassemble into new continental configurations over hundreds of millions of years, driven by the dynamics of plate tectonics and mantle convection. Understanding these models helps geologists interpret the supercontinent cycle—a fundamental process shaping the evolution of the planet’s surface, climate, and biosphere.

Background: The Supercontinent Cycle

The Earth’s continents have repeatedly aggregated into large landmasses called supercontinents, which later fragmented and drifted apart. This process, known as the supercontinent cycle, operates on a timescale of roughly 400–600 million years.
Major supercontinents recognised in geological history include:

• Columbia (Nuna): ~1.8–1.5 billion years ago
• Rodinia: ~1.1 billion–750 million years ago
• Pannotia: ~600 million years ago
• Pangaea: ~335–175 million years ago

The breakup and reassembly of these landmasses are influenced by deep mantle processes, subduction zones, and plate motions. The Orthoversion and Introversion models attempt to explain where and how a new supercontinent forms relative to the location of its predecessor.

The Introversion Model

Introversion (meaning “turning inward”) describes a model in which a new supercontinent forms by the closing of the internal ocean basin created during the breakup of its predecessor.
Concept and Mechanism:

• When a supercontinent breaks apart, it creates two major types of ocean basins:
  1. Internal oceans – those that form between the newly rifted continental fragments.
  2. External oceans – pre-existing oceans surrounding the former supercontinent.
• In the introversion model, subduction zones develop along the internal ocean margins, gradually closing these newly formed internal oceans.
• The drifting continental fragments eventually reunite over the same site as the previous supercontinent.

Example: The classic example of introversion is the formation of Pangaea (~335 million years ago). It formed through the closure of the Iapetus Ocean, which had opened during the breakup of Rodinia. The continents that once drifted apart from Rodinia converged inward again to reassemble as Pangaea—essentially over the same location as their ancestor supercontinent.
Key Features of the Introversion Model:

• New supercontinent forms at or near the site of the previous one.
• Driven primarily by inward subduction of internal ocean basins.
• Mantle convection beneath the supercontinent site is long-lived and relatively stable.
• Represents a direct recycling of continental configuration.

Geological Evidence:

• Paleomagnetic data show that many continents involved in Pangaea’s formation had previously drifted outward from the Rodinia configuration.
• Orogenic belts (mountain chains) such as the Appalachians and Caledonides formed through collisions closing internal oceans, consistent with introversion.

The Orthoversion Model

The Orthoversion Model represents a newer concept proposed to explain supercontinent assembly that occurs neither directly inward (introversion) nor entirely outward (extroversion), but instead at right angles (orthogonal) to the previous supercontinent’s configuration.
Concept and Mechanism:

• After a supercontinent breaks apart, the internal ocean opens, and subduction zones develop around its periphery.
• Over time, the subduction zones and mantle convection patterns reorganise, and convergence begins along great circles approximately 90° away from the geographic centre of the previous supercontinent.
• The new supercontinent forms at a position orthogonal (perpendicular) to that of the previous one, hence the term orthoversion.

Example:

• The transition from Rodinia (~900–750 million years ago) to Pangaea (~335 million years ago) is often cited as an example of orthoversion.
• Paleomagnetic and geological reconstructions suggest that Pangaea formed roughly 90° away from the equatorial position of Rodinia.
• Similarly, the hypothesised future supercontinent Amasia, expected to form in 200–300 million years, may assemble near the Arctic region, roughly orthogonal to Pangaea’s former site.

Key Features of the Orthoversion Model:

• The next supercontinent forms roughly 90° from the previous one’s location.
• Involves reorganisation of mantle convection and global plate motions.
• Indicates that mantle upwelling and downwelling zones shift laterally with time.
• Reflects a more dynamic, global-scale interaction between plate and mantle processes.

Geological Evidence:

• Paleomagnetic reconstructions show a near-orthogonal shift in the positions of continental masses between Rodinia and Pangaea.
• Deep mantle seismic tomography indicates that supercontinent centres correspond to mantle upwellings, which evolve laterally over time due to changes in heat flow and subduction dynamics.

Comparative Analysis: Introversion vs. Orthoversion

Relation to the Extroversion Model

For context, a third model—Extroversion—complements the other two. In the extroversion scenario, a new supercontinent forms by closing the external ocean surrounding the previous supercontinent, while the internal ocean continues to expand. For example, if the Atlantic Ocean (internal to Pangaea’s breakup) continues to widen while the Pacific (external) closes, a future supercontinent could form through extroversion.
Thus, the three models describe alternative pathways for supercontinent evolution:

• Introversion: Inward reassembly (closure of internal oceans).
• Extroversion: Outward reassembly (closure of external oceans).
• Orthoversion: Orthogonal reassembly (90° from previous supercontinent).

Implications for Earth’s Geodynamics

These models have far-reaching implications for understanding Earth’s interior and surface evolution:

1. Mantle Convection and Heat Flow: The cyclic assembly and breakup of supercontinents are closely linked to mantle convection patterns. Orthoversion suggests that mantle upwelling zones (superplumes) migrate laterally, altering global heat distribution and tectonic processes.
2. Supercontinent Longevity: The position of a supercontinent over a long-lived mantle upwelling (as in introversion) may influence its stability and eventual breakup.
3. Climate and Biosphere: Supercontinent formation affects global climate by altering ocean circulation, atmospheric CO₂ levels, and biodiversity patterns.
4. Mineral and Resource Distribution: The cyclic assembly of continents influences orogeny, volcanism, and mineral deposition, shaping Earth’s economic geology.

Current and Future Supercontinent Predictions

Based on modern plate movements and mantle dynamics, scientists predict the formation of a future supercontinent, variously named Amasia, Aurica, or Novopangaea, depending on the model applied:

• Amasia (Orthoversion): Continents converge around the Arctic, ~90° from Pangaea’s former site.
• Aurica (Extroversion): The Pacific closes while the Atlantic opens further.
• Novopangaea (Introversion): Continents reconvene over the equatorial region where Pangaea once existed.