PLATE TECTONICS A Summary & Review GEOL 1033 Lecture ppt file ) (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 Columbia Southern 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 Margin Trailing Edge Continental Margin “head” “tail”

DISTRIBUTION OF PASSIVE CONTINENTAL MARGINS Trailing Edge Continental Margins

FEATURES OF PASSIVE CONTINENTAL MARGINS 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

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READING ASSIGNMENTS - Revised 26 Oct., th Edition, 2003, Sverdrup & others, pages correspond to lesson topics in the Study Guide: –Lesson 1page 2 –Lesson 2p , –Lesson 8p (Q7 assigned) –Lesson 3p (E3 assigned) –Lesson 4p. 2-21, 24-26(Q3 assigned) –Lesson 5p ; 3(bottom+fig)-4(fig); 259(bottom)-260(top)(Q4 assigned) –Lesson 6p , 87-89, 364(gases) –Lesson 7p (top), , (sound),120(bottom)-124 (Q6 assigned) –Lesson 9 p , 101(bathymetry)-112(fig) –Lesson 10 p. “ “ “ “ –Lesson 11 p. “ “ “ “ (Q9 assigned) –Lesson 12 p. “ “ “ “, 107(fig+bottom)-110(top), –Lesson 13 p. “ “ “ “ –Lesson 14 p. 112(sediments)-127 (Q11 assigned) –Lesson 15 p –Lesson 37 p , (Q27 assigned) –Lesson 16 p , 65 (E9 assigned) –Lesson 17 p. 64(fig), 66, 73-75, 127(Min Dep), 87, 90-96, –Lesson 18 p , 81(hot spots)-83 –Lesson 19 p –Lesson 20 “ “ “ –Lesson 21 p , (Q13 assigned) 6 th edition, (2000), or 5 th edition, (1997) may be used. Ask for handout for pages to be studied. Test #1 Test #2