Lecture 23

The earth was made so various,That the mind of desultory man, studious of change

And pleased with novelty, might be indulged

- Wm. Cowper (The Task, 1785)

Plate Tectonics

Webpage for course (daytime)

Webpage for course (nighttime)

Alfred WegnerMeteorologist “Doesn't the east coast of South America fit exactly against the west coast of Africa, as if they had once been joined?” (1910, letter to his fiancee)

http://www.jazclass.aust.com/blog/files/drift.htm

http://geology.com/pangea.htm

Why was Wegner’s ideas not accepted?

Acceptance of Wegner’s theory

Early 1960s

Sea Floor spreading

Subduction

Tests for Wegner’s theorySea Floor spreading

Age of igneous bedrock

Subduction

Benioff zones

Glomar Challenger Deep Sea Drilling Project, 1968-83

JOIDES ResolutionOcean Drilling Program, 1985-2006 refurbished and back at sea, early 2009

Deep Sea Drilling

“continental drift” vs. “plate tectonics

PlatesContinental crust

thicker (~50 km)

older

less dense

Oceanic crust

thinner (~10 km)

younger than 200 myr

more dense

Mix (ex. North American Plate)

MarginsDivergent

Convergent

Transverse

Divergent boundary, Atlantic Oc.

Kevin-drawing, Convergent, Pac.

Convergent, continent-continent

transverse

California