Prof. John J. Renton
Outline Lecture Notes** (JA)
- Plate tectonics has revolutionised our understanding of geology since 1965.
- Earth cooled into inner core (heaviest), mantle and crust (lightest).
- Liquid rock called magma below surface, lava above.
- Siiica content of magma (granitic = 75%, basaltic = 45%) determines its viscosity. Basaltic like olive oil, granitic like molasses.
- Thinner basaltic magma rose faster and spread out over surface. Granite hit surface later and formed islands in basalt.
- Water vapour from magma formed cloud cover until surface temps allowed rain to fall and settle.
- Idea that continental outlines fitted together and were once joined not well received in WW1. No energy source or mechanism to split continents.
- WW2 SONAR mapping showed network of oceanic ridges, rather than flat plain, also trenches parallel to coasts, with associated volcanic arcs
- Geomagnetism studies revealed mirror-image pattern of magnetic reversal on either side of ridges - implying ocean floor spreading.
- Crust creation at ridges requires consumption elsewhere to maintain earth's size - trenches are where crust is forced down under continents (subduction) and melts to cause volcanic arcs.
- Seismic studies showed plastic layer (asthenosphere) 100-250 miles down. Convection currents in this layer move plates above, along with continents. Up-currents spread ocean floor, down-currents drive subduction, providing both energy and mechanism for continental drift.
- Entire plates move, taking continents with them. When continents collide, mountains are formed.
|Plate Tectonics||description [Wikipedia]|
|Alfred Wegener||life and works [Wikipedia]|
|Continental Drift theory||description [Wikipedia]|
|Structure of Earth||description [Wikipedia]|
**more detailed lecture notes available to group members on request.