Plutonic‐Squishy Lid: A New Global Tectonic Regime Generated by Intrusive Magmatism on Earth‐Like Planets

Abstract

The thermal and chemical evolution of rocky planets is controlled by their surface tectonics and magmatic processes. On Earth, magmatism is dominated by plutonism/intrusion versus volcanism/extrusion. However, the role of plutonism on planetary tectonics and long-term evolution of rocky planets has not been systematically studied. We use numerical simulations to systematically investigate the effect of plutonism combined with eruptive volcanism. At low-to-intermediate intrusion efficiencies, results reproduce the three common tectonic/convective regimes as are usually obtained in simulations using a viscoplastic rheology: stagnant-lid (a one-plate planet), episodic (where the lithosphere is usually stagnant and sometimes overturns into the mantle), and mobile-lid (similar to plate tectonics). At high intrusion efficiencies, we observe a new additional regime called "plutonic-squishy lid." This regime is characterized by a set of small, strong plates separated by warm and weak regions generated by plutonism. Eclogitic drippings and lithospheric delaminations often occur close to these weak regions, which leads to significant surface velocities toward the focus of delamination, even if subduction is not active. The location of the plate boundaries is strongly time dependent and mainly occurs in regions of magma intrusion, leading to small, ephemeral plates. The plutonic-squishy-lid regime is also distinctive from other regimes because it generates a thin lithosphere, which results in high conductive heat fluxes and lower internal mantle temperatures when compared to a stagnant lid. This regime has the potential to be applicable to the Early Archean Earth and present-day Venus, as it combines elements of both protoplate tectonic and vertical tectonic models. Plain Language SummaryThe evolution of Earth-like planets is controlled by the dynamics of their rigid outer part, called the lithosphere, and magmatic processes. Studies of terrestrial magmatic processes show that most melt is intruded into the crust. However, the effect of intrusive magmatism on the long-term evolution of rocky planets has not been systematically studied. Here we use numerical models to simulate global mantle convection in a rocky planet. When eruptions dominate, our results reproduce the three tectonic regimes found in previous studies: mobile lid, similar to plate tectonics operating on modern-day Earth; stagnant lid or a planet covered by a single plate; and episodic lid where the planet is covered by one plate that resurfaces into the mantle more or less frequently. For high intrusion efficiencies, we describe the new "plutonic-squishy-lid" regime. Hot intrusions make the lithosphere squishy and lead to drippings and delaminations of the crust. In turn, these processes lead to significant surface velocities (even if subduction is not active), and small, short-lived plates. The lithosphere is kept thin, and therefore, the loss of heat from the interior is efficient. The new regime has the potential to be applicable to the Archean Earth and ...

Implications of Anomalous Crustal Provinces for Venus' Resurfacing History

“…This would not align with Venus' upper mantle viscosity constraints from gravity and topography observations (Rolf et al, 2018; Steinberger et al, 2010). A thinner crustal layer in the stagnant lid regime may still be possible, though, in particular by considering crustal intrusions (Lourenço et al, 2018, 2020) and/or by using a stronger temperature dependence of viscosity (larger activation energy); we could not employ either of these measures because of numerical feasibility. In contrast, the episodic lid models generate crustal thicknesses in the range of 20–120 km depending on the frequency of overturns and especially the time passed since the latest overturn (Figure 4).…”

“…Thus, mantle temperatures may be lower than observed in our models. Intrusive magmatism also leads to a warmer and weaker lithosphere (Rozel et al, 2017), which could in turn facilitate overturn events or even promote a different tectonic regime (Lourenço et al, 2020).…”

Reviewing subduction initiation and the origin of plate tectonics: What do we learn from present-day Earth?

“…It has been well established from geodynamic modeling that stagnant‐lid convection is likely the dominant mode for silicate planets, due to the strongly temperature‐dependent viscosity of rocks (Moresi and Solomatov, 1995, 1998). This prediction, together with observations confirming the prevalence of stagnant‐lid convection on silicate planets, suggests that Earth might have evolved through a stagnant‐lid phase before its current plate‐tectonics phase (Sleep, 2000; Stern, 2007), although some authors suggest that a variant squishy‐lid regime was present before the start of plate tectonics (Johnson et al, 2014; Rozel et al, 2017; Lourenço et al, 2020). Therefore, an understanding of the transition from stagnant‐lid convection to plate‐tectonics convection, i.e.…”

101 Geodynamic modelling: How to design, interpret, and communicate numerical studies of the solid Earth

“…When a generic modelling philosophy is applied, a general geodynamic feature is investigated via a parameter study, where a certain parameter space is mapped out and can be represented by a so-called regime diagram (e.g., Lourenço et al, 2020).…”

“…One way of doing that is to model subduction and its surface response, and vary all key subduction parameters over their individual Earth-like ranges as done in e.g., Crameri et al (2017). Other generic modelling examples are quantifying crustal thickness at mid-ocean ridges for various spreading velocities (e.g., Katz, 2008), reproducing general magma dynamics (e.g., Spiegelman, 1993) or magma transport behaviour (e.g., Yamato et al, 2012), the onset of convection in a planetary mantle (Turcotte and Schubert, 2012, section 6.19), testing for what Rayleigh numbers and Clapeyron slopes a phase transition induces layered convection (e.g., Christensen and Yuen, 1985), quantifying the amount of entrainment of a dense layer into mantle plumes (e.g., Lin and van Keken, 2006a, b;Jones et al, 2016), investigating the plate tectonic regimes of a planet, which might range from a stagnant lid with only one plate to a mobile lid, similar to modern plate tectonics (e.g., Petersen et al, 2017;Lourenço et al, 2016;Lourenço et al, 2020), investigating under which conditions the flow in the Earth's outer core would cause an Earth-like dynamo (Christensen, 2011;Christensen and Wicht, 2015;Wicht and Sanchez, 2019), and mapping out the dominance of inner-core convection, rotation, or translation depending on its viscosity and conductivity (e.g., Deguen et al, 2013).…”