The diversity of tectonic modes and thoughts about transitions between them

Abstract

Plate tectonics is a particular mode of tectonic activity that characterizes the present-day Earth. It is directly linked to not only tectonic deformation but also magmatic/volcanic activity and all aspects of the rock cycle. Other terrestrial planets in our Solar System do not operate in a plate tectonic mode but do have volcanic constructs and signs of tectonic deformation. This indicates the existence of tectonic modes different from plate tectonics. This article discusses the defining features of plate tectonics and reviews the range of tectonic modes that have been proposed for terrestrial planets to date. A categorization of tectonic modes relates to the issue of when plate tectonics initiated on Earth as it provides insights into possible pre-plate tectonic behaviour. The final focus of this contribution relates to transitions between tectonic modes. Different transition scenarios are discussed. One follows classic ideas of regime transitions in which boundaries between tectonic modes are determined by the physical and chemical properties of a planet. The other considers the potential that variations in temporal evolution can introduce contingencies that have a significant effect on tectonic transitions. The latter scenario allows for the existence of multiple stable tectonic modes under the same physical/chemical conditions. The different transition potentials imply different interpretations regarding the type of variable that the tectonic mode of a planet represents. Under the classic regime transition view, the tectonic mode of a planet is a state variable (akin to temperature). Under the multiple stable modes view, the tectonic mode of a planet is a process variable. That is, something that flows through the system (akin to heat). The different implications that follow are discussed as they relate to the questions of when did plate tectonics initiate on Earth and why does Earth have plate tectonics. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics’.

A non–plate tectonic model for the Eoarchean Isua supracrustal belt

“…Prior studies suggest that in such a scenario, mantle convective forcing would have overcome the strength of a single plate lithosphere, involving this lithosphere in the convection process (e.g., Kankanamge and Moore, 2016;Moore and Webb, 2013;Moresi and Solomatov, 1998). Once involved, a large fraction of the existing lithosphere would have rapidly subducted due to its weight and been replaced by juvenile lithosphere of sufficient youth and corresponding buoyancy to resist subduction, thereby temporarily reestablishing a single plate lithosphere (presumably cooling via hot stagnant lid, plume-dominated cooling, as described in Lenardic's [2018] classification scheme). Future work may examine possible tectonic evolutions, such as (1) if the Isua rocks represent the workings of an early single plate lithosphere exclusively, with the Eoarchean shearing representing an Io-analogous shortening event, or (2) if the deformation experienced at Isua between 3.7 Ga and 3.66-3.60 Ga records a crustal response to a subduction episode, and the Barberton and Pilbara greenstone belts reflect the renewed, slower development of a single plate lithosphere.…”

“…3.2-2.5 Ga. The most common hypothesis to explain this shift is the onset of plate-tectonic recycling following some form of hot stagnant lid geodynamics (e.g., Lenardic, 2018). However, a focus on tectono-metamorphic geology highlights a finding that contradicts this overall interpretation.…”

Geological archive of the onset of plate tectonics

“…In significant part, these reflect differences in what might be regarded as the onset of plate tectonics, and how best to recognize plate tectonics in the geological record. A variety of non-plate tectonic modes related to evolving tectonothermal environments have been observed or proposed for other bodies in the solar system and for the early Earth ([ 6 ] and references therein). Those advocating a pre-plate tectonic regime for the early Earth generally invoke a fixed or episodically mobile lithosphere, often referred to as a stagnant-lid, but perhaps more appropriately as a single-lid.…”

Paleomagnetic evidence for modern-like plate motion velocities at 3.2 Ga

“…These structural and compositional differences have led to a number of proposals that the Archean crust was constructed by exotic processes, including plume tectonics (5,6), sagduction/drip tectonics (6,7), and a vertically overturning lithosphere (8,9). Since some of these processes are difficult to reconcile with plate mobility, alternative geodynamical regimes have been proposed for the Archean Earth, including stagnantlid and sluggish-lid modes (10,11) in which the lithosphere was rendered immobile, or at least slowed, due to decoupling from the asthenosphere under elevated geothermal gradients (12). Other studies argue for a uniformitarian model of the Archean Earth, in which some variant of modern plate tectonics was in operation at least locally throughout Earth history (13).…”