Plate Tectonics
Plate tectonics is the unifying theory of geology, describing the Earth's rigid outer shell as a mosaic of moving plates whose interactions build mountains, open oceans, and trigger earthquakes and volcanism.
Definition
Plate tectonics is the theory that the lithosphere is divided into a small number of rigid plates that move relative to one another over the weaker, ductile asthenosphere, with most geological activity concentrated along plate boundaries.
Scope
This area covers the lithospheric plates and their relative motions, the evidence that established the theory (continental fit, paleomagnetism, seafloor spreading), the three classes of plate boundary, the forces that drive plate motion, and the long-term assembly and breakup of continents. It frames the kinematics and dynamics of plates rather than the internal physics of the deep Earth, which belongs to geophysics.
Sub-topics
Core questions
- How many lithospheric plates are there, and how fast do they move relative to one another?
- What lines of evidence demonstrate that continents move and oceans grow?
- What forces drive and resist plate motion?
- How do plate configurations change over hundreds of millions of years?
Key theories
- Plate tectonics (the new global tectonics)
- Earth's lithosphere behaves as a set of rigid plates whose relative motions on a sphere are described by rotations about Euler poles; deformation and seismicity concentrate at plate margins while plate interiors remain largely undeformed.
- Transform faults
- Wilson identified transform faults as a distinct class of plate boundary that links spreading ridges and trenches, reconciling offset ridge segments and predicting the sense of motion later confirmed by earthquake studies.
Mechanisms
Plates form at mid-ocean ridges where new oceanic lithosphere is created, cool and thicken as they age, and are recycled into the mantle at subduction zones. Their motion is governed primarily by slab pull at subducting margins and ridge push at spreading centers, with basal drag from mantle flow acting as either a driver or resistance depending on the flow regime.
Clinical relevance
Plate tectonics underpins the assessment of seismic and volcanic hazard, the prediction of where earthquakes and eruptions cluster, and the exploration logic for many mineral and hydrocarbon deposits whose distribution tracks past plate boundaries.
History
The idea that continents move was proposed by Alfred Wegener in 1912 but rejected for lacking a mechanism. Mid-twentieth-century advances in paleomagnetism, ocean-floor mapping, and the discovery of magnetic-stripe symmetry led Harry Hess to propose seafloor spreading. Between 1965 and 1968, Wilson, McKenzie and Parker, Morgan, and Le Pichon formalized the rigid-plate model, completing the plate-tectonic revolution.
Debates
- Relative roles of slab pull versus ridge push and basal drag
- The partitioning of plate-driving forces among slab pull, ridge push, and mantle drag remains debated, with most analyses favoring slab pull as dominant but disagreeing on the contribution of active mantle convection.
Key figures
- Alfred Wegener
- Harry Hess
- J. Tuzo Wilson
- Dan McKenzie
- W. Jason Morgan
- Xavier Le Pichon
Related topics
Seminal works
- wilson1965
- mckenzieparker1967
- morgan1968
Frequently asked questions
- What is the difference between continental drift and plate tectonics?
- Continental drift was Wegener's early claim that continents move but it lacked a mechanism. Plate tectonics is the modern theory that explains how: rigid lithospheric plates carrying both continents and ocean floor move over the asthenosphere, created at ridges and consumed at trenches.
- How fast do tectonic plates move?
- Plates move at rates of roughly one to ten centimeters per year, comparable to the growth rate of human fingernails, with fast-spreading oceanic plates moving faster than slow continental ones.