Plate Tectonics and Earthquakes Natural Disasters, 5th edition, Chapter 3

Plate Tectonics I.The Discovery of Plate Tectonics II.The Mosaic of Plates III.Rates and History of Motion IV.Mantle Convection

I. Discovery of Plate Tectonics A.Continental Drift B.Seafloor Spreading

A. Continental Drift 1.Continental drift: large-scale movements of continents

A. Continental Drift (continued) 2.Support a.Puzzle fit 1.Suess (1900)- Gondwana 2.Wegner (1915)- Pangea

A. Continental Drift (continued) b.Similar rock ages c.Similar geologic structures d.Fossil Evidence e.Climate Evidence

B. Seafloor Spreading 1.Convection currents move plates around 2.Mantle source 3.Post-WWII: Mid- Atlantic Ridge 4.Hess & Dietz (1960’s) propose new and recycled seafloor

II. The Mosaic of Plates A.Lithospheric Plates B.Divergent Boundaries C.Convergent Boundaries D.Transform-Fault Boundaries

A. Lithospheric Plates 1.Mosaic of large moving plates 2.Geologic activities occur at plate boundaries a.Earthquakes b.Volcanoes c.Rifts d.Folding e.Faulting

B. Divergent Boundaries 1.Narrow rifts 2.Continental plate separation 3.Oceanic plate separation- spreading centers

Divergent Boundaries Oceanic Plate Separation Mid- Atlantic Ridge North American Plate North American Plate Eurasian Plate Eurasian Plate

Divergent Boundaries Oceanic Plate Separation Mid- Atlantic Ridge North American Plate North American Plate Eurasian Plate Eurasian Plate Volcanoes and earthquakes concentrate.

Divergent Boundaries Continental Plate Separation East African Rift Valley Somali Subplate African Plate

Divergent Boundaries Continental Plate Separation East African Rift Valley Somali Subplate African Plate Parallel valleys; volcanoes and earthquakes.

C. Convergent Boundaries 1.Conservation of Earth’s surface area 2.Ocean-ocean convergence 3.Ocean-continent convergence 4.Continent-continent convergence

Convergent Boundaries Ocean-Ocean Convergence Mariana Islands Marianas Trench Pacific Plate Philippine Plate Philippine Plate

Convergent Boundaries Ocean-Ocean Convergence Mariana Islands Marianas Trench Pacific Plate Philippine Plate Philippine Plate Deep-sea trench; volcanic island arc.

Convergent Boundaries Ocean-Continent Convergence Nazca Plate Andes Mountains South American Plate South American Plate Peru-Chile Trench

Convergent Boundaries Ocean-Continent Convergence Nazca Plate Andes Mountains South American Plate South American Plate Peru-Chile Trench A volcanic belt of mountains forms.

Convergent Boundaries Continent-Continent Convergence Himalaya Main thrust fault Tibetan Plateau Indian-Australian Plate Eurasian Plate Eurasian Plate

Convergent Boundaries Continent-Continent Convergence Himalaya Main thrust fault Tibetan Plateau Indian-Australian Plate Eurasian Plate Eurasian Plate Crust crumbles, creating high mountains and a wide plateau.

D. Transform-Fault Boundaries 1.Plates slide past one another 2.Fracture with relative displacement

Transform-Fault Boundaries Mid-Ocean Ridge Transform Fault North American Plate Eurasian Plate

Transform-Fault Boundaries Mid-Ocean Ridge Transform Fault North American Plate Eurasian Plate Spreading centers offset.

Transform-Fault Boundaries Continental Transform Fault North American Plate Pacific Plate

Transform-Fault Boundaries Continental Transform Fault North American Plate Pacific Plate Offset continental crust.

As plates move past each other...

As plates move past each other... …creek beds are offset

As plates move past each other... …creek beds are offset San Francisco Los Angeles San Andreas fault

III. Rates and History of Motion A.Seafloor Magnetic Tape Recorder B.Geodesy

A. Seafloor Magnetic Tape Recorder 1.Magnetic reversals a.Switching strength to the south b.Preserved in lava c.Age can be dated d.Magnetic chrons- ½ million years e.Magnetic subchrons – years

Magnetic anomalies also in volcanic lava.

Normal Reversed

Magnetic anomalies also in volcanic lava. Normal Reversed Earth’s magnetic field reverses direction. Layers “remember”. Older layers preserve their direction. Scientists constructed a magnetic time scale.

Gilbert reversed chron Gauss normal chron Matuyama reversed chron Brunhes normal chron 5.0 MaPresent Subchrons

Mid-ocean ridge Ocean crust today Million years ago (Ma) 5.0 million years old

A. Seafloor Magnetic Tape Recorder (continued) 2.Magnetic anomaly a.Normal-positive anomaly b.Reverse-negative anomaly 3.Seafloor ages a. Speed = distance / time

Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. Mid-Atlantic Ridge High intensity Low intensity

Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. Mid-Atlantic Ridge High intensity Low intensity A sensitive magnetometer records magnetic anomalies,…

Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. Mid-Atlantic Ridge High intensity Low intensity A sensitive magnetometer records magnetic anomalies,… Iceland Mid- Atlantic Ridge

Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. Mid-Atlantic Ridge High intensity Low intensity A sensitive magnetometer records magnetic anomalies,… Iceland Mid- Atlantic Ridge …alternating bands of high and low magnetism. Symmetrical bands on both sides. Why?

B. Geodesy 1.Astronomical Positioning a.Position with respect to fixed stars b.100 m error 2.Global Positioning a.24 Earth-orbiting satellites b.Measure plate movement

IV. Mantle Convection A.Driving Forces B.Plate Recycling C.Convection Currents

A. Driving Forces 1.Mantle convection 2.Gravitational pull

B. Plate Recyling 1.New lithosphere- ridges 2.Old lithosphere- subduction 3.Recycling within upper and lower mantle-seismic waves

Whole-mantle convection Upper mantle Lower mantle 700 km 2900 km Outer core Mantle Outer core Inner core

Whole-mantle convection Upper mantle Lower mantle 700 km 2900 km Outer core

Stratified convection Boundary near 700 km separates the two convection systems.

C. Convection Currents 1.Movement of lithospheric plates 2.Mantle plumes a.Hot spots b.Deep mantle

Plate Tectonics I.The Discovery of Plate Tectonics II.The Mosaic of Plates III.Rates and History of Motion IV.Mantle Convection