Dissecting the puzzle of tectonic lid modes in terrestrial planets

The dynamics of the coupled plate-mantle system control planetary thermal evolution, crustal geology and geo-morphology, dynamo action, as well as atmospheric evolution and habitability. Rocky planets within our solar system display a diverse array of tectonic regimes, despite their similar origins. Among them, Earth is unique in exhibiting plate tectonics, or a “mobile lid”. Several bodies, such as Mars and the Moon, display a tectonically inactive surface, or a “stagnant lid”. An episodic lid or plutonic-squishy lid has been suggested for Venus, and a sluggish lid for early Mars. The conditions that give rise to these regimes and their transitions throughout planetary evolution remain poorly understood.

To address this challenge, we here explore 2D thermochemical mantle-convection models with self-consistent crustal formation and lithospheric yielding. In a broad parameter study, we examine the influence of core-mantle boundary temperature, internal heating rate, upper-mantle activation energy, and effective yield stress on mantle dynamics and surface tectonics. In each model, we analyze the long-term statistics of tectonic characteristics (mobility and plateness) in the statistical steady state in order to quantitatively distinguish between various tectonic regimes. Such an effort that has been previously complicated by the transient nature of planetary evolution. Thereby, we identify a previously unrecognized episodic-squishy lid regime that is characterized by alternating episodes of plutonic-squishy lid and mobile-lid behavior. By systematically exploring the parameter space, we develop a regime diagram that predicts the tectonic evolution of terrestrial planets as they cool over time. Our findings offer a comprehensive framework for understanding the tectonic history of Earth-like planets, shedding light on their surface conditions and interior evolution.