Chapter 2: Plate Tectonics

Tectonic Plates of Earth

Pangaea Pangaea: Pan = all Gaea = Earth Panthalassa Thalassa = sea AKA Tethys Sea Pangaea: Pan = all Gaea = Earth Panthalassa Thalassa = sea AKA Tethys Sea

Continental Drift Progressive breakup of Pangaea into modern continents Similar to sea ice Progressive breakup of Pangaea into modern continents Similar to sea ice

Wegner’s Evidence Present-day shorelines fit like puzzle pieces Better fit from continental shelves Present-day shorelines fit like puzzle pieces Better fit from continental shelves

Fossil Evidence Identical fossils present in S. Amer. & Africa e.g. Mesosaurus e.g. Glossopteris e.g. Marsupials Identical fossils present in S. Amer. & Africa e.g. Mesosaurus e.g. Glossopteris e.g. Marsupials

Geologic Evidence Identical rocks on different continents e.g. 2.2Ga igneous rocks in Brazil & Africa Similar Mountain Ranges e.g. Appalachian Mts ~ Caledonian Mts Identical rocks on different continents e.g. 2.2Ga igneous rocks in Brazil & Africa Similar Mountain Ranges e.g. Appalachian Mts ~ Caledonian Mts

Mesozoic Supergroup Identical package of rocks & fossils found in S.Amer., Africa, Australia & Antarctica

Paleoclimatic Evidence Paleo = ancient Climate = weather conditions Glacially transported sediments Glacial striations Paleo = ancient Climate = weather conditions Glacially transported sediments Glacial striations

Rejection of Continental Drift Hypothesis No evidence of continents “breaking through” oceanic crust Tidal forces necessary would halt Earth’s rotation Danish scientists found no astronomical evidence of drift from No evidence of continents “breaking through” oceanic crust Tidal forces necessary would halt Earth’s rotation Danish scientists found no astronomical evidence of drift from

Earth’s Magnetic Field Similar to bar magnet Magnetic materials align themselves to magnetic field Similar to bar magnet Magnetic materials align themselves to magnetic field

N-S Orientation & Dip Magnetic orientation has 2 dimensions North-South Dip angle (Inclination) Curie point (T) Fossil Magnetism / Paleomagnetism Magnetic orientation has 2 dimensions North-South Dip angle (Inclination) Curie point (T) Fossil Magnetism / Paleomagnetism

Magnetic Inclination Magnetization = degrees from N pole Magnetization + Latitude = 90° e.g. Lavas from Puerto Rico show 75 ° from N pole & Puerto Rico = 15 ° from equator Magnetization = degrees from N pole Magnetization + Latitude = 90° e.g. Lavas from Puerto Rico show 75 ° from N pole & Puerto Rico = 15 ° from equator

Apparent Polar Wander

Seafloor Spreading

Paleomagnetism

Progression of Seafloor Spreading

Plate Boundaries

Corresponds to Earthquakes & Volcanoes

Plate Boundaries Three Types Divergent AKA Rift Convergent AKA Subduction Transform AKA Strike-slip Three Types Divergent AKA Rift Convergent AKA Subduction Transform AKA Strike-slip

Divergent Boundaries AKA Spreading Centers AKA Rifts Largest mountain chains Plates move apart due to eruption of lava New lava = new oceanic crust Oldest oceanic crust 180Ma AKA Spreading Centers AKA Rifts Largest mountain chains Plates move apart due to eruption of lava New lava = new oceanic crust Oldest oceanic crust 180Ma

Pillow Basalts Form when lava extruded under water Immediately outer layer freezes New material pushes through like toothpaste Form when lava extruded under water Immediately outer layer freezes New material pushes through like toothpaste

Continental Rifting Rifts also can form in continental settings Linear depressions Lakes, valleys, etc. Asthenosphere thins due to tension e.g. East Africa Rift Zone, Mt. Kilimanjaro Rifts also can form in continental settings Linear depressions Lakes, valleys, etc. Asthenosphere thins due to tension e.g. East Africa Rift Zone, Mt. Kilimanjaro

Continental Rifting (con’t) If tension continues, eventually continental rift develops into oceanic spreading e.g. Red Sea, Sea of Cortez If tension continues, eventually continental rift develops into oceanic spreading e.g. Red Sea, Sea of Cortez

Convergent Boundaries Old oceanic crust dense & heavy Heavy vs. light => subduction AKA destructive margins Large earthquake & explosive volcanoes Melting triggered at ~100km depth Old oceanic crust dense & heavy Heavy vs. light => subduction AKA destructive margins Large earthquake & explosive volcanoes Melting triggered at ~100km depth

Oceanic-Oceanic Convergence e.g. Virgin Islands, Japan, Philippines

Oceanic-Continental e.g. Andes, MesoAmerica, Italy

Continental-Continental e.g. India

Hot Spots Caused by mantle plumes Plumes do not move, plates do Bend at 40Ma Major change in plate motion Caused by mantle plumes Plumes do not move, plates do Bend at 40Ma Major change in plate motion

Relative Plate Motions Relative to Hot Spots & other plates Measure motions with Paleo- magnetism Relative to Hot Spots & other plates Measure motions with Paleo- magnetism

Forces Driving Plate Motions Convection of Mantle Upwelling Mantle Ridge- push Slab Suction AKA Slab- pull Convection of Mantle Upwelling Mantle Ridge- push Slab Suction AKA Slab- pull

Layer-Cake Model Two zones of convection, above & below ~660km Explains why mid-ocean ridge basalt different than hot spot basalt Two zones of convection, above & below ~660km Explains why mid-ocean ridge basalt different than hot spot basalt

Whole Mantle Convection Cold oceanic crust descend to bottom of mantle, “stirring” it Hot plumes rise from core-mantle boundary Bring “primitive” mantle to surface Not popular b/c complete mixing in 100s Ma Cold oceanic crust descend to bottom of mantle, “stirring” it Hot plumes rise from core-mantle boundary Bring “primitive” mantle to surface Not popular b/c complete mixing in 100s Ma

Deep Layer Model Heat from Earth’s interior causes two layers to shrink & swell Similar to lava lamp Small amt of material rises to surface to create hot spots Little seismic evidence to support this model Heat from Earth’s interior causes two layers to shrink & swell Similar to lava lamp Small amt of material rises to surface to create hot spots Little seismic evidence to support this model

Importance of Plate Tectonics First theory to provide comprehensive view & explain: Earth’s major surficial processes Geologic distribution of earthquakes, volcanoes & mountain ranges Distribution of mineral resources & ancient organisms First theory to provide comprehensive view & explain: Earth’s major surficial processes Geologic distribution of earthquakes, volcanoes & mountain ranges Distribution of mineral resources & ancient organisms