Transcript 103-19-ContDrift&PlateTectSum

PLATE TECTONICS
A Summary & Review
GEOL 1033
Lecture ppt file 103-19)
(Lesson 21)
PANGAEA - about 250 Ma ago
• CONTINENTAL
DRIFT THEORY:
• Wegener, 1915
• Pangaea:
– Laurasia
– Gondwanaland
• evidence:
– geographic fits,
similar rocks,
similar ages,
similar structures,
similar fossils,
similar climates,
similar ancient
environments
Bullard's STATISTICAL CONTINENTAL FIT
• 95% fit is excellent
ages
basins
structures
DISTRIBUTION OF CONTINENTAL FOSSILS
• Glossopteris flora of southern hemisphere
• Reptile fossils of the southern hemisphere
ANCIENT GLACIATIONS
• Glacial deposits of southern hemisphere match
WEGENER'S BREAKUP OF PANGAEA
• Pangaea began to rift & drift apart about 200 Ma ago
Note India
OCEANOGRAPHY of 1960’s
• supported continental
evidence for drift theory:
– Seafloor topography
– Deep-sea sediments
– Micropaleontology
– Paleooceanography
– Seafloor spreading
– Plate tectonics
MODEL OF THE SOUTHERN ATLANTIC
• Seafloor topography became much better understood
PALEOMAGNETISM OF THE OCEAN BASINS
• Interpretation of magnetic polar reversals:
– Confirms seafloor spreading
– Dates ocean basins
TRANSFORM BOUNDARIES DISCOVERED
In addition to divergent and convergent zones.
Active:
British Columbia
Southern California
(Passive:
Southern Margin of Grand Banks)
Leading edge continental margins
UNDERSTANDING OF THE TRENCH
REGIONS OF THE WORLD
• Leading Edge Continental Margins
Deep-Sea Trenches & their plate tectonic significance
• Subduction zones
OVERVIEW OF PLATE TECTONIC PROCESSES
•
Converging zone
Diverging zone
Transform faults offseting oceanic ridge axis
“ocean to ocean”
Converging Zone
oceanic ridge
Diverging Zone
“ocean to continent”
Converging Zone
DRIVING MECHANISM for PLATE TECTONICS is
THERMAL CONVECTION in EARTH'S INTERIOR
FORMATION OF SEAMOUNTS & TABLEMOUNTS
• Thermal contraction of lithosphere once seafloor
spreads away from heat source results in subsidence of
older seafloor far from spreading ridge
SUBSIDENCE OF SEAFLOOR WITH AGE
• Topographic data plotted with theoretical models
BASAL SEDIMENT AGES
• Base of sediments above basalt increase in age away
from spreading ridge
• Core studies confirmed seafloor spreading
FUTURE OF SOUTH ATLANTIC
• South America & Africa will continue to separate
LITHOSPHERIC PLATE BOUNDARIES
• 1) Spreading centers (=divergence zones)
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Ridges & rises of ocean floors
Shallow earthquakes
Volcanism
New lithosphere formation
2 kinds: Oceanic & continental
• 2) Transform faults
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Lateral translation & shear
Two kinds: active & passive
Some volcanism (active vs. passive)
Shallow earthquakes (active vs. passive)
• 3) Converging zones
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Shallow to deep earthquakes
Subduction & trenches
Volcanism & magmatic arcs (volcanic island arcs & volcanic mountain belts)
Mountain-building
Metamorphism
Plate collisions (3 kinds)
2 KINDS OF Diverging Zones
• Oceanic
– New
• Gulf of Aden
• Red Sea rift
• Gulf of California
– Mature
•
•
•
•
Mid-Atlantic Ridge
East pacific rise
Juan de Fuca Ridge
Carlsburg Ridge
• Continental
– East African Rift Valley system
– Mesozoic (Triassic-Jurassic) basins of eastern North America
3 KINDS OF PLATE COLLISIONS
• 3 kinds of lithospheric plate collisions
– a) Oceanic to oceanic (western Pacific examples)
– b) Oceanic to continental (eastern Pacific examples)
– c) Continental to continental (India colliding with southern Asia)
PLATE TECTONIC CLASSIFICATION
OF CONTINENTAL MARGINS
• 1) TRAILING EDGE = divergent = passive = aseismic = Atlantic
• 2) LEADING EDGE = convergent = active = seismic = Pacific
• 3) TRANSFORM FAULT = translational
– Occur along:
• trailing edge continental margins and
• leading edge continental margins
– There are two kinds:
• active
• passive
Trailing Edge Continental Margin
Leading Edge Continental Margin
“head”
“tail”
DISTRIBUTION OF PASSIVE CONTINENTAL MARGINS
Trailing Edge
Continental Margins
FEATURES OF PASSIVE CONTINENTAL MARGINS
sediments
sediments
Eastern North America is a
trailing edge continental margin
WESTERN CANADA HAS A
COLLISION/TRANSFORM BOUNDARY
Northern British Columbia:
Active transform fault
Southern British Columbia:
Leading edge continental margin
END OF FILE
READING ASSIGNMENTS - Revised 26 Oct., 2003
Test #2
Test #1
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7th Edition, 2003, Sverdrup & others, pages correspond to lesson topics in the Study Guide:
– Lesson 1
page 2
– Lesson 2
p. 29-38, 45-51
– Lesson 8
p. 54-59
(Q7 assigned)
– Lesson 3
p. 38-42
(E3 assigned)
– Lesson 4
p. 2-21, 24-26
(Q3 assigned)
– Lesson 5
p. 40-45; 3(bottom+fig)-4(fig); 259(bottom)-260(top)
(Q4 assigned)
– Lesson 6
p. 42-45, 87-89, 364(gases)
– Lesson 7
p. 99-101(top),108-109,143-144(sound),120(bottom)-124 (Q6 assigned)
– Lesson 9 p. 62-63, 101(bathymetry)-112(fig)
– Lesson 10 p. “
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– Lesson 11 p. “
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(Q9 assigned)
– Lesson 12 p. “
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, 107(fig+bottom)-110(top), 464-465
– Lesson 13 p. “
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– Lesson 14 p. 112(sediments)-127
(Q11 assigned)
– Lesson 15 p. 393-413
– Lesson 37 p. 393-413, 374-379
(Q27 assigned)
– Lesson 16 p. 53-61, 65
(E9 assigned)
– Lesson 17 p. 64(fig), 66, 73-75, 127(Min Dep), 87, 90-96, 468-469
– Lesson 18 p. 71-79, 81(hot spots)-83
– Lesson 19 p. 64-71
– Lesson 20 “ “ “
– Lesson 21 p. 83-86, 95-96
(Q13 assigned)
6th edition, (2000), or 5th edition, (1997) may be used. Ask for handout for pages to be studied.