Influence of plate tectonic mode on the coupled thermochemical evolution of Earth's mantle and core

Abstract

We investigate the influence of tectonic mode on the thermochemical evolution of simulated mantle convection coupled to a parameterized core cooling model. The tectonic mode is controlled by varying the friction coefficient for brittle behavior, producing the three tectonic modes: mobile lid (plate tectonics), stagnant lid, and episodic lid. The resulting compositional structure of the deep mantle is strongly dependent on tectonic mode, with episodic lid resulting in a thick layer of subducted basalt in the deep mantle, whereas mobile lid produces only isolated piles and stagnant lid no basaltic layering. The tectonic mode is established early on, with subduction initiating at around 60 Myr from the initial state in mobile and episodic cases, triggered by the arrival of plumes at the base of the lithosphere. Crustal production assists subduction initiation, increasing the critical friction coefficient. The tectonic mode has a strong effect on core evolution via its influence on deep mantle structure; episodic cases in which a thick layer of basalt builds up experience less core heat flow and cooling and a failed geodynamo. Thus, a continuous mobile‐lid mode existing from early times matches Earth's mantle structure and core evolution better than an episodic mode characterized by large‐scale flushing (overturn) events.

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

“…Over the years, numerical simulations run using different codes and employing different degrees of complexity have provided consistent results: In general, when a viscoplastic, strongly temperature‐dependent rheology is used, three convective regimes with different surface expressions are found. These are mobile lid for low yield stresses, episodic lid for intermediate yield stresses, and stagnant lid for high yield stresses (Lourenço et al, ; Moresi & Solomatov, ; Nakagawa & Tackley, ; O'Neill et al, ; Tackley, ). Figure shows the mantle final thermal and compositional states of one example of these regimes, obtained through the simulations run in the present study (Figure c depicts a new regime described later in this work).…”

“…It shows that an enriched mantle (Figure c) is more efficient at cooling the mantle than a depleted mantle (Figures b and d) (cf. Bédard, ; Nakagawa & Tackley, ). Figure shows an overview of how basaltic material is distributed in the mantle by the end of the simulations performed in this study.…”

Long‐Term Stability of Plate‐Like Behavior Caused by Hydrous Mantle Convection and Water Absorption in the Deep Mantle

“…For the dry mantle, pulse-like profiles are found in the surface heat flow and surface mobility charts for the first several 100 Myr, followed by near-zero mobility, which indicates a nearly "stagnant lid" convection. For the hydrous mantle, the surface heat flow is higher than that of the dry mantle by a factor of 2, and surface mobility indicates nearly stable plate motion that would suitably explain the style of surface tectonic motion on the Earth (e.g., Nakagawa & Tackley, 2015). Figure 3 shows the thermo-chemical-viscous-hydrous structure in the mantle 4.6 Gyr after the initial conditions with friction coefficients of 0.1 (Figure 3, left), 0.175 (Figure 3, middle), and 0.3 (Figure 3, right).…”

Venus: A Thick Basal Magma Ocean May Exist Today

“…The core contained 50 ppm of potassium (e.g., Hirose et al, ) and precipitated light elements at a rate of ~10 19 kg/K or 5 × 10 −6 K −1 normalized to the mass of the core (e.g., Badro et al, ; O'Rourke & Stevenson, ). Finally, Q BMO decreased linearly from 55 TW at the start to 15 TW at present, which approximates the cooling history obtained using boundary layer models (e.g., Blanc et al, ; Labrosse et al, ; Ziegler & Stegman, ) and dynamical simulations (e.g., Nakagawa & Tackley, , ).…”