PLATE TECTONICS

A Summary & ReviewGEOL 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

basins

structures

ages

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

Active:British ColumbiaSouthern California

(Passive: Southern Margin of Grand Banks)

Leading edge continental margins

In addition to divergent and convergent zones.

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

oceanic ridge Diverging Zone

“ocean to ocean” Converging 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)

– Ridges & rises of ocean floors– Shallow earthquakes– Volcanism– New lithosphere formation– 2 kinds: Oceanic & continental

• 2) Transform faults– Lateral translation & shear– Two kinds: active & passive– Some volcanism (active vs. passive)– Shallow earthquakes (active vs. passive)

• 3) Converging zones– 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

Leading Edge Continental MarginTrailing 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 atrailing 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• 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. “ “ “ “ – Lesson 11 p. “ “ “ “ (Q9 assigned)– Lesson 12 p. “ “ “ “ , 107(fig+bottom)-110(top), 464-465– Lesson 13 p. “ “ “ “– 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.

Tes

t #1

Tes

t #2