Transcript Slide 1

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)
Lecture 23
Alfred Wegner
Meteorologist
“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 theory
Sea Floor spreading
Age of igneous bedrock
Subduction
Benioff zones
Deep Sea Drilling
Glomar Challenger
Deep Sea Drilling Project, 1968-83
JOIDES Resolution
Ocean Drilling Program, 1985-2006
refurbished and back at sea, early 2009
“continental drift” vs. “plate tectonics
Plates
Continental crust
thicker (~50 km)
older
less dense
Oceanic crust
thinner (~10 km)
younger than 200 myr
more dense
Mix (ex. North American Plate)
Margins
Divergent
Convergent
Transverse
Divergent boundary, Atlantic Oc.
Kevin-drawing, Convergent, Pac.
Convergent, continent-continent
transverse
California