Chapter 19 Plate Tectonics

1
Chapter 19Plate Tectonics
2
Current Plate Boundaries and Relative Motion
3
The Early Case for Continental Drift

• Skepticism about Continental Drift
• Paleomagnetism and the Revival of Continental
  Drift
• Recent Evidence for Continental Drift
• History of Continental Positions

4
Plate Motion Animation
5
Plate Reconstructions
6
Fossil Evidence for Gondwana
Early Triassic
Permian
Permian-Pennsylvanian
7
Distribution of Paleozoic Glaciers and Glacial
Striations
8
Polar Wander Hypotheses
9
Wegeners Reconstruction of Apparent South Polar
Wander Path
NB that Wegener believed that the continents
moved, not the pole!
10
Polar Wander Hypotheses

• From paleoclimatic evidence, Wegener found that
  the apparent position of the poles (and therefore
  equator) had moved through geological time.
• Possible interpretations
• Continents were motionless and poles actually
  moved
• Poles were motionless and continents moved
• Both occurred - most likely scenario

11
Wegeners Concept of Continental Drift and
Orogenesis
Most geologists and geophysicists rejected
Wegeners ideas because they violated what was
known about the strength of rocks. Also,
centrifugal force (from Earths rotation) along
with tidal forces were deemed to be too small to
move the continents!
12
Paleomagnetism - Revival of Continental Drift
13
Apparent Geomagnetic Pole
14
Magnetic Polar Wander Paths
Best interpretation is that there was a single
magnetic pole and North America and Europe
separated in the Late Triassic forming the
Atlantic Ocean basin
15
Goodness of Fit of the 100 m depth contour
Lithological and age correlation for rock units
Glacial striae
Continental Shelves
16
Sea-Floor Spreading

• Hesss Driving Force
• Explanations
• Plates and Plate Motion

17
Hess Heat Engine
18
Lithosphere vs. Asthenosphere
19
How Do We Know That Plates Move?

• Marine Magnetic Anomalies
• Magnetic Stripe Map
• Another Test Fracture Zones and Transform Faults
• Euler Poles of Rotation
• Measuring Plate Motion Directly
• Space Geodesy
• VLBI
• GPS
• DORIS

20
Marine Magnetic Anomalies
21
Magnetic Time Scale
22
Magnetic Stripe Formation at Ridge Crest
23
Age vs. Magnetic Polarization
24
Sea Floor Age Map
25
GPS Global Velocity Field
26
Typical GPS Time Series and SCIGN Mount
CGPS Site SCMS
JPL Time Series for Yellowknife, CA
Photo credit http//www.scign.org/