Download Physical Geology 1330 Dr. Mike Murphy

Physical Geology 1330
116-S&R 1
Ocean Floor and Seafloor Spreading
Dr. Mike Murphy
[email protected]
333-S&R-1
www.uh.edu/~mamurph2/homepage.html
Today’s Outline
Continental Drift
Seafloor Spreading
Movie: “The birth of a theory”
Continental Drift – the hypothesis that the continents once fit together to form a
supercontinent and have since drifted apart to their present positions.
Evidence Supporting the Continental Drift Hypothesis
1.
2.
3.
4.
What caused the continents to drift?
Why was the Continental Drift hypothesis rejected?
Seafloor Spreading - The process whereby plates move apart and magma wells up into
newly created fractures and generates new slivers of oceanic lithosphere
Evidence supporting Seafloor Spreading
1.
2.
3.
What didn’t the Seafloor Spreading hypothesis explain?
Paleomagnetism - The study of natural remnant magnetization preserved in rocks in
order to determine the intensity and direction of the Earth’s magnetic field in the geologic
past
Earth’s Magnetic Field
This angle is called
the inclination
When Fe-rich minerals cool below their Curie Point they become magnetized in in a
direction parallel to the existing magnetic lines of force
Curie point - the temperature at which a mineral become magnetized (~580 C).
Two kinds of data paleomagnetism provides are:
1.
2.
Polar Wandering –
Geomagnetic Reversals –
Normal polarity –
Reverse polarity –
Magnetic Stripes – parallel stripes of normally and reversely magnetized rock present on
the seafloor and symmetric about mid-ocean ridges.
Paleomagnetic Time Scale – established by measuring the magnetic polarity of lava
flows of known age.
Spreading Rate at a Mid-Ocean Ridge
Plate Tectonics1. A model explaining how the Earth works.
2. A set of ideas explaining the observed motion of Earth’s lithosphere through the
mechanisms of subduction and seafloor spreading, which in turn, generate Earth’s major
features, including continents and ocean basins (T&L).
The strong, rigid lithosphere, which lies above the weak asthenosphere, is broken into
several plates.
Plates are continuously changing their shape and size because of deformation at their
boundaries.
Seven Major Plates are recognized:
1. North American
2. South American
3. Pacific
4. African
5. Eurasian
6. Australian
7. Antarctic
Plate Boundaries (Divergent, Convergent, Transform)
Divergent Boundary –
Convergent Boundary –
Transform Boundary –
Divergent Boundary Evolution –
Early Stage referred to as ________________.
Later Stage referred to as ________________________.