Geodynamics and Mantle Convection
Geodynamics applies the physics of deforming solids and fluids to the Earth, explaining plate tectonics, mantle convection, and the slow flow that drives mountain building, earthquakes, and volcanism.
Definition
Geodynamics is the study of the forces and processes that drive motion and deformation in the solid Earth, applying continuum mechanics, fluid dynamics, and heat transport to phenomena such as plate tectonics and mantle convection.
Scope
This area covers the dynamics of the solid Earth: plate tectonics as the surface expression of mantle convection, the rheology and thermal convection of the mantle, the strength and deformation of the lithosphere, and the continuum mechanics of stress, strain, and heat transport that govern all of these. It treats the forces that drive plate motion, the styles and vigor of mantle flow, and the long-term evolution of the planet's thermal and mechanical state. The emphasis is on the physical processes that move and deform the solid Earth over geological time.
Sub-topics
Core questions
- What forces drive the plates, and how does plate tectonics work on a sphere?
- How does the solid mantle convect, and what controls its vigor and style?
- How does the strength and rheology of the lithosphere shape deformation?
- How do stress, strain, and heat transport govern solid-Earth dynamics?
Key concepts
- Plate tectonics and plate boundary forces
- Mantle convection and the Rayleigh number
- Mantle and lithospheric rheology
- Stress, strain, and continuum mechanics
- Thermal evolution of the Earth
Key theories
- Plate tectonics
- The lithosphere is divided into rigid plates that move over the weaker asthenosphere, interacting at spreading ridges, subduction zones, and transform faults; McKenzie and Parker showed plate motions obey rigid rotation on a sphere, unifying continental drift and seafloor spreading.
- Thermal mantle convection
- The mantle, though solid, creeps over geological time and convects to remove the Earth's internal heat; the vigor of convection, governed by the Rayleigh number, organizes upwellings and downwellings that drive plate motions.
Clinical relevance
Geodynamics provides the explanatory framework for earthquakes, volcanism, mountain building, and the distribution of natural resources, and informs long-term hazard assessment and our understanding of the thermal and tectonic evolution of the Earth and other planets.
History
Wegener proposed continental drift in 1912 and Holmes suggested mantle convection as its engine, but only in the 1960s did seafloor spreading and the rigid-plate kinematics of McKenzie, Parker, and Morgan establish plate tectonics, after which quantitative geodynamics and mantle-convection modeling matured.
Key figures
- Alfred Wegener
- Arthur Holmes
- Dan McKenzie
- Donald Turcotte
Related topics
Seminal works
- turcotte2014
- schubert2001
- mckenzie1967
Frequently asked questions
- How can the solid mantle flow and convect?
- Over millions of years rock deforms like an extremely viscous fluid through the slow migration of crystal defects, so although the mantle is solid on human timescales, it creeps and convects on geological ones, transporting heat and driving plate motion.
- What drives the motion of tectonic plates?
- Plates are driven mainly by forces tied to mantle convection, especially the pull of cold, dense subducting slabs sinking into the mantle and the push at spreading ridges, with the whole system organized by the convective removal of the Earth's internal heat.