From plumes to subduction network formation and supercontinent break-up

Supercontinents, mantle dynamics and plate tectonics: A perspective based on conceptual vs. numerical models

Fifty years ago, Tuzo Wilson published his paper asking ‘Did the Atlantic close and then re-open?’. This led to the ‘Wilson Cycle’ concept in which the repeated opening and closing of ocean basins along old orogenic belts is a key process in the assembly and breakup of supercontinents. The Wilson Cycle underlies much of what we know about the geological evolution of the Earth and its lithosphere, and will no doubt continue to be developed as we gain more understanding of the physical processes that control mantle convection, plate tectonics, and as more data become available from currently less accessible regions. This volume includes both thematic and review papers covering various aspects of the Wilson Cycle concept. Thematic sections include: (1) the Classic Wilson v. Supercontinent Cycles, (2) Mantle Dynamics in the Wilson Cycle, (3) Tectonic Inheritance in the Lithosphere, (4) Revisiting Tuzo's question on the Atlantic, (5) Opening and Closing of Oceans, and (6) Cratonic Basins and their place in the Wilson Cycle.

This review discusses the thermal evolution of the mantle following large-scale tectonic activities such as continental collision and continental rifting. About 300 myr ago, continental material amalgamated through the large-scale subduction of oceanic seafloor, marking the termination of one or more oceanic basins (e.g. Wilson cycles) and the formation of the supercontinent Pangaea. The present day location of the continents is due to the rifting apart of Pangaea, with the dispersal of the supercontinent being characterized by increased volcanic activity linked to the generation of deep mantle plumes. The discussion presented here investigates theories regarding the thermal evolution of the mantle (e.g. mantle temperatures and sub-continental plumes) following the formation of a supercontinent. Rifting, orogenesis and mass eruptions from large igneous provinces change the landscape of the lithosphere, whereas processes related to the initiation and termination of oceanic subduction have a profound impact on deep mantle reservoirs and thermal upwelling through the modification of mantle flow. Upwelling and downwelling in mantle convection are dynamically linked and can influence processes from the crust to the core, placing the Wilson cycle and the evolution of oceans at the forefront of our dynamic Earth.

Mantle Dynamics: An Introduction and Overview

Role of the overriding plate in the subduction process

This volume brings together contributions from the Royal Society Discussion Meeting on ‘Earth dynamics and the development of plate tectonics' held in March 2018. Other planets in the Solar System do not exhibit plate tectonics, so why does it occur on Earth, how did it develop and when did Earth adopt this tectonic regime? In evaluating evidence from the geological record, it is critical to distinguish between local and global phenomena in a discussion of the why, how and when of the transition to plate tectonics on Earth. Thus, evidence of local or episodic subduction in the geological record, for example, does not necessarily provide evidence for the development of a sustainable global network of mobile belts that forms the basis for a mosaic of plates. The tectonic regime at any point in the evolution of a planet appears to depend on the initial conditions set by crystallization of the last magma ocean. These conditions determine the thermal state—‘hot’ or ‘cold’—at the start of sub-solidus mantle convection, which is subsequently driven by the relative contributions of basal and internal heating to the mantle through time. Plate tectonics is linked to the ability of mantle convection to form plate boundaries, which requires localized weakening of the lithospheric lid. How and when did this become possible? Consideration of the tectonic regime on Venus, which may be an analogue for the early tectonic development of Earth, evidence from the rock record, rock deformation experiments, geodynamic models extrapolated back to the thermal conditions appropriate to the Archaean, and geochemical models for the development and growth of the continental crust have led to the currently popular view that plate tectonics developed from a stagnant lid regime. However, if mantle convection is able to form weak plate boundaries at the higher mantle temperatures expected during the …

Crustal evolution recommenced after the Late Heavy bombardment caused melting and mixing of the Hadean crust. Upwelling hot mantle spread out carrying the colder brittle crust away from the upwelling current causing rifts and lateral movement of crustal plates. Partial melting due to the reduction of pressure on the mantle generated magma that flowed through the rifts forming new crust while degassing of the magma produced the atmosphere and hydrosphere. New information from the Yilgarn craton in Western Australia indicates that where the lateral movement of converging plates intersected the crust was compressed into multi-kilometre scale folds. Partial melting at the base of the folded crust produced granodiorite and a dense ultramafic restite and the formation of an Archean style craton. The spreading mantle flow loses heat through the crust becoming denser and together with the restite sinks down through the mantle forming a convective cycle. When two cratons approach the intervening mafic crust is folded forming a new craton that joins the cratons into a continent. Mantle plumes rising beneath the continent cause rifts to open and the formation of new ocean crust in the rifts while older ocean crust is subducted beneath the outer margins of the continent.

Permo–Triassic intraplate magmatism and rifting in Eurasia: implications for mantle plumes and mantle dynamics

Large salt accumulations as a consequence of hydrothermal processes associated with ‘Wilson cycles’: A review, Part 2: Application of a new salt-forming model on selected cases

What drives the breakup of a supercontinent remains contentious. Previously proposed mechanisms include mantle plumes, subduction retreat and basal traction from mantle convection. Here we review the geological record of plumes, orogens and subduction zones during the breakup of Pangaea and investigate the potential roles played by these factors through 4D spherical geodynamic modelling. We found that mantle plumes provided the dominant force that drove the breakup of Pangaea, particularly in triggering the initial breakup. Young orogens as continental lithospheric weak zones generally guided the development of continental rifts, consistent with the geological record that rifting within Pangaea commonly developed along pre-existing orogens. However, the marginal drag force produced by subduction retreat, and basal traction associated with subduction-related mantle flow, likely also played a role in the breakup of Pangaea. In addition, the weakening effect of plume-induced melts can sometimes help to break the continental lithosphere away from orogens, as exemplified by the breakup between Antarctica and Australia. Furthermore, geodynamic modelling suggests that subduction is responsible for generating mantle plumes. A particular such example is the formation of the Kerguelen plume, triggered by subduction along the northern margin of Australia, which facilitated the breakup between East Antarctica and Australia.

A leading tool for understanding thermal convection in the Earth’s mantle is numerical modeling. To solve Boussinesq equations a finite element code has been applied. This is the first time this method has been used in Hungary, namely, modeling mantle convection on the Cartesian coordinate system. The simulations have been run in 2D Cartesian and cylindrical coordinate systems as well as in a “mantle-like” cylindrical-shell. The mantle dynamics are controlled by the Rayleigh number, which is the ratio of the buoyancy to viscous forces. The effect of Ra has been studied in the range of 1e4 to1e7. The significance of the cylindrical geometry is that at a given rms velocity the convection can carry the most heat to the surface and the results were close to the three dimensional case. This may imply that the upwelling part of the 3D mantle convection is cylindrical (mantle plume). In the cylindrical-shell domain an impressive approximate picture of the chaotic structure of the mantle convection has been shown. With the comparison of the three geometries it could be said that the cylindrical coordinate-system seems to be the most appropriate geometry to investigate the physical properties of an individual mantle plume.

LIPs, orogens and supercontinents: The ongoing saga

Mantle Dynamics Past, Present, and Future: An Introduction and Overview

7.01 - Mantle Dynamics Past, Present, and Future: An Introduction and Overview

For plate tectonics to operate on a planet, mantle convective forces must be capable of forming weak, localized shear zones in the lithosphere that act as plate boundaries. Otherwise, a planet's mantle will convect in a stagnant lid regime, where subduction and plate motions are absent. Thus, when and how plate tectonics initiated on the Earth is intrinsically tied to the ability of mantle convection to form plate boundaries; however, the physics behind this process are still uncertain. Most mantle convection models have employed a simple pseudoplastic model of the lithosphere, where the lithosphere 'fails' and develops a mobile lid when stresses in the lithosphere reach the prescribed yield stress. With pseudoplasticity high mantle temperatures and high rates of internal heating, conditions relevant for the early Earth, impede plate boundary formation by decreasing lithospheric stresses, and hence favour a stagnant lid for the early Earth. However, when a model for shear zone formation based on grain size reduction is used, early Earth thermal conditions do not favour a stagnant lid. While lithosphere stress drops with increasing mantle temperature or heat production rate, the deformational work, which drives grain size reduction, increases. Thus, the ability of convection to form weak plate boundaries is not impeded by early Earth thermal conditions. However, mantle thermal state does change the style of subduction and lithosphere mobility; high mantle temperatures lead to a more sluggish, drip-like style of subduction. This 'sluggish lid' convection may be able to explain many of the key observations of early Earth crust formation processes preserved in the geologic record. Moreover, this work highlights the importance of understanding the microphysics of plate boundary formation for assessing early Earth tectonics, as different plate boundary formation mechanisms are influenced by mantle thermal state in fundamentally different ways.This article is part of a discussion meeting issue 'Earth dynamics and the development of plate tectonics'.