1. Plate Tectonics

2. Earth’s tectonic plates
(move at speeds ranging from 1 to 15 cm per year, as determined from magnetic isochrons or time lines, laser ranging or GPS techniques)

3. Hawaiian Island and Emperor Seamount Chain
Besides active volcanism associated with ridges and subduction zones, intra-plate volcanism can result in the formation of volcanic ranges.

4. The Hawaiian Islands
From:

5. The Hawaiian hot spot and absolute plate velocity
The islands and submarine seamounts have been dated by the K/Ar method and found to increase in age with distance from Kilauea.
From: Skinner & Porter (1999) The Dynamic Earth

6. Tuzo Wilson’s concept of a “hot spot”
Tuzo Wilson proposed that hot-spot volcanoes develop over a long-lived magma source originating deep within the mantle.

7. Plate
motion
Active
volcano 3
Extinct
volcano 2
Seamount
of volcano 1
Moving lithosphere
Asthenosphere
Mantle
plume
Time
Hot-spot volcanoes are probably a consequence of mantle plumes. As a plate drifts over the hotspot, a chain of extinct volcanoes (a "hot-spot track") forms, allowing a determination of the absolute velocity of the lithospheric plate.
Over time, a hot-spot volcanic island erodes and subsides, eventually sinking below sea level to form a seamount. Guyots are flat-topped seamounts.

8. Hawaiian Island and Emperor Seamount Chain
35+ Myrs
For at least the last 5 million years, a new island has emerged every million years.
Loihi
40 Myrs

9. Loihi: A new Hawaiian Island in the making

10. Hot spots of the world! (over 100 have been identified, of which about 40 remain active)

11. Relative and absolute plate motions

12. Two-layer convection model – W. Jason Morgan’s view (circa 1971)
Mantle Convection
The rate at which heat reaches the Earth’s surface can only be accounted for if convection (unlike conduction) in the mantle brings heat from the deep interior.
... but it is impossible to draw a global arrangement of convection cells that can explain the complex geometry of plate boundaries.
Jason Morgan suggested that the ascending currents coming from deep in the mantle are the driving force of mantle convection and, therefore, of plate tectonics.
Two-layer convection model – W. Jason Morgan’s view (circa 1971)

13. Ridge push and/or slab pull?
Spreading edge
At first, it was thought that rising magma at a spreading center creates new lithosphere, and in the process it pushes the plates sideways.

14. Ridge push and/or slab pull?
Alternatively, it has been suggested that plate motion is driven by the attitude of the ridges and the subduction of older oceanic lithosphere
Hence, the upward movement of the asthenosphere beneath the mid-ocean ridge and the intrusion of magma are a consequence of seafloor spreading rather than the cause.

16. Slab pull

17. Slab-pull on the steel roof of my country cottage

18. Wadati-Benioff zone – subduction earthquakes
Earthquakes in the vicinity of subduction zones are mostly extensional, as if something was pulling the plate The spreading rate and the length of subduction zones are correlated, supporting the hypothesis that subduction is responsible for spreading.

19. Plate Tectonics summary
Convection keeps the asthenosphere hot and weak by bringing up heat from the deep mantle and the core. As a result, the lithospheric plates can slide on the plastic mantle (the asthenosphere) as they are pulled to subduction zones.

20. Plate Tectonics summary