Earth dynamics and the development of plate tectonics.

Abstract

This volume brings together contributions from the Royal Society Discussion Meeting on ‘Earth dynamics and the development of plate tectonics' held in March 2018. Other planets in the Solar System do not exhibit plate tectonics, so why does it occur on Earth, how did it develop and when did Earth adopt this tectonic regime? In evaluating evidence from the geological record, it is critical to distinguish between local and global phenomena in a discussion of the why, how and when of the transition to plate tectonics on Earth. Thus, evidence of local or episodic subduction in the geological record, for example, does not necessarily provide evidence for the development of a sustainable global network of mobile belts that forms the basis for a mosaic of plates. The tectonic regime at any point in the evolution of a planet appears to depend on the initial conditions set by crystallization of the last magma ocean. These conditions determine the thermal state—‘hot’ or ‘cold’—at the start of sub-solidus mantle convection, which is subsequently driven by the relative contributions of basal and internal heating to the mantle through time. Plate tectonics is linked to the ability of mantle convection to form plate boundaries, which requires localized weakening of the lithospheric lid. How and when did this become possible? Consideration of the tectonic regime on Venus, which may be an analogue for the early tectonic development of Earth, evidence from the rock record, rock deformation experiments, geodynamic models extrapolated back to the thermal conditions appropriate to the Archaean, and geochemical models for the development and growth of the continental crust have led to the currently popular view that plate tectonics developed from a stagnant lid regime. However, if mantle convection is able to form weak plate boundaries at the higher mantle temperatures expected during the …