Integrated study of lid modes and plate tectonic patterns in planetary evolution : diversity, commonalities, and evolutionary mechanisms

Abstract

The Earth and other terrestrial planets in the solar system (Mercury, Venus, Mars) share similar compositions and internal structures. Although some scholars have recently proposed that there is evidence of plate tectonics on Mars, the mainstream view still holds that Earth is the only planet with active plate tectonics. The various lithosphere dynamics patterns exhibited by planets are commonly referred to as "tectonic regimes" or "lid regimes." Despite numerous studies on planetary lid regimes, controversies remain, particularly regarding the formation and potential transformation of various lid modes and the origin of Earth's plate tectonics. This doctoral project aims to investigate various tectonic convection patterns through numerical simulations of Earth's geodynamics and to study the initiation and causes of Earth's unique plate tectonics by combining geological and environmental evidence. First, we establish a whole-mantle scale convection model to simulate the state of a planet's interior and its lid. The model includes melting and crustal production and assumes a high intrusion rate. We conduct a parameter sensitivity analysis for lithosphere strength, upper mantle rheology, and endogenic heat, which yielded mobile lid, sluggish lid, episodic lid, plutonic-squishy lid, stagnant lid, and a new lid regime called episodic-plutonic lid. The episodic-plutonic lid is similar to the traditional episodic lid, but lacks a stagnant phase which is replaced by a plutonic-squishy lid. Moreover, we can infer the potential evolution of planetary lids (hot to cold) and the uniqueness of the dynamic environment that allows plate tectonics to occur from the simulation results. Subsequently, we set up a high-resolution model with a sticky-air layer for Earth to better observe and study the impact of mantle convection on the local lithosphere. We choose a homogeneous chemical composition without melting to thoroughly investigate the mechanical influence of convection on the lid. By changing the lithosphere strength and mantle activation, we discover an episodic lid between mobile and stagnant lids, with its initiation time and plate tectonics cycle varying with parameters. According to our numerical simulation, there may be two episodes of plate (mobile-lid) tectonics emerging from the stagnant-lid mode, lasting from 2.16 Ga to 1.64 Ga, and from 0.75 Ga to the present, respectively. It is the first time using a continuous mantle convection model to demonstrate the existence of two-episode plate tectonics on Earth. Our findings reveal that these two mobile-lid stages not only reconcile the major geological records on Earth but also demonstrate close associations with the environment and climate. The stagnant-lid stage, sandwiched between the two mobile-lid episodes, also echoes the widely debated "boring billion" in tectonics. In addition, the global overturning event at the onset of each plate tectonics episode in the simulation provides a novel explanation for the scarcity of Precambrian geological records.