New Tectonic Regime Found on Earth, Venus

An international team led by researchers from the Department of Earth and Planetary Sciences at The University of Hong Kong (HKU), including postdoctoral fellow Dr Tianyang LYU, Professor Man Hoi LEE (also with the Department of Physics), and Mok Sau-King Professor Guochun ZHAO, has made a significant breakthrough in understanding the tectonic evolution of terrestrial planets. Using advanced numerical models, the team systematically classified for the first time six distinct planetary tectonic regimes and identified a novel regime: the "Episodic-Squishy Lid". The study not only provides crucial clues to the origin of Earth's plate tectonics but also offers a robust theoretical framework for deciphering the enigmatic geological features of Venus. The findings have been published in the journal Nature Communications.

Six Tectonic Regimes Revealing Planetary Evolution Pathways

Terrestrial planets exhibit diverse tectonic regimes, referring to the large-scale deformation of their surface layers and the processes that generate such deformation. These regimes directly shape a planet's geological activity, internal evolution, magnetic field, atmospheric composition, and even its potential to harbour life. One of the most enduring mysteries in planetary science is why Earth exhibits active plate tectonics while its "sister planet" Venus has a starkly different geological character.

The way a planet's surface deforms is a key factor in determining its evolution. For example, Mars displays a tectonically inactive "stagnant lid" regime, resulting in a largely immobile surface that preserves ancient impact craters. In contrast, Earth operates under a "mobile lid" (plate tectonic) regime, with a network of mid-ocean ridges, transform faults and subduction zones. While these plate boundaries give rise to geological hazards such as earthquakes and volcanism, they have helped to stabilise Earth's atmospheric and climatic conditions over millions and billions of years, fostering the evolution of life. For example, climate-active compounds such as CO₂ or water can be buried in the Earth's interior as oceanic sediments are subducted due to plate tectonics, but can likewise be recycled to the atmosphere at volcanoes after long-term storage in the mantle, leading to roughly balanced surface conditions.

Past studies proposed additional tectonic regimes such as the "sluggish lid" or "plutonic-squishy lid", but the relationships among these regimes —and their connections to terrestrial planets—remained unclear. "Through statistical analysis of vast amounts of model data, we were able to identify six tectonic regimes for the first time quantitatively," explained Dr Tianyang LYU, the first author of the paper. "These include the mobile lid (like modern Earth), the stagnant lid (like Mars), and our newly discovered 'episodic-squishy lid'. This new regime is characterised by an alternation between two modes of activity, offering a fresh perspective on how planets transition from an inactive to an active state."

Decoding the "Memory Effect": Unlocking the Tectonic Signatures of Planets

A major challenge in predicting a planet's tectonic evolution has been the "memory effect", or hysteresis, where a planet's tectonic state depends not only on its current conditions but also on its long history. "Our models reveal that this 'memory effect' is not insurmountable," explained Professor Man Hoi LEE. "Especially on an evolutionary path where the lithosphere weakens over time — as is the case for Earth — the transition between tectonic regimes can be surprisingly predictable. This finding significantly enhances the predictive power of our framework."

The research team also constructed a comprehensive diagram mapping all six tectonic regimes under different physical conditions, revealing the likely transition pathways as a planet cools over time. Professor Guochun ZHAO, who is also an Academician of the Chinese Academy of Sciences, added, "Geological records suggest that tectonic activity on early Earth aligns with the characteristics of our newly identified regime. As Earth gradually cooled, its lithosphere became more prone to fracturing under specific physical mechanisms, eventually leading to today's plate tectonics. This provides a key piece of the puzzle in explaining how Earth became a habitable planet."

The findings also offer a compelling explanation for the enigmatic geology of Venus. The models show that some surface features on Venus, such as the >1,000 km wide, circular "coronae", are highly consistent with the "plutonic-squishy lid" or "episodic-squishy lid" regimes. In these regimes, magmatic intrusions weaken the lithospheric lid, leading to regional, intermittent tectonic activity dominated by mantle plumes, rather than global plate-boundary–driven deformation. Professor Zhong-Hai LI of the University of Chinese Academy of Sciences, a co-author of the study, noted, "It is exciting to compare our model results with geological observations of Venus. This provides important theoretical references and observational targets for future Venus missions."

This research establishes a new framework for classifying and understanding of planetary tectonic diversity, providing tools for future planetary exploration. "Our models intimately link mantle convection with magmatic activity," concluded Dr Maxim D BALLMER of University College London, another co-author of the study. "This allows us to view the long geological history of Earth and the current state of Venus within a unified theoretical framework, and it provides a crucial theoretical basis for the search for potentially habitable Earth analogues and super-Earths outside our solar system."

For more details, please refer to the journal paper "Dissecting the puzzle of tectonic lid regimes in terrestrial planets" published in Nature Communications: https://doi.org/10.1038/s41467-025-65943-1