Plate Tectonics (Wrong kind of plate…and where’s my salad fork?)

The crust is broken!

We measure plate motion with GPS

Continental Drift Whiplash

Plate Boundary Types

Divergent plate boundary

2 plates are moving AWAY from each other2 plates are moving AWAY from each other Seen in mid-ocean ridgesSeen in mid-ocean ridges and rift valleys and rift valleys Where in the world?

Divergent plate boundary (forming a rift valley)

Mid ocean ridge

Divergent plate boundary Features: 1) 1) 2) 2) 3) 3)

Divergent plate boundary Features: 1)Mid ocean ridges 2)Undersea volcanoes—may make islands 3)Rift valleys, on land

Convergent plate boundaries

2 plates move TOWARD each other2 plates move TOWARD each other

What is happening at the plate boundary? Oceanic Plate

Subduction When 2 plates converge, one plate MAY move downwards UNDER the other – this is called SUBDUCTIONWhen 2 plates converge, one plate MAY move downwards UNDER the other – this is called SUBDUCTION

Subduction Earthquakes are deeper the farther inland you go.

Subduction Accretion—some of the lightest oceanic crust joins the continent

Which plate is subducting?Which plate is subducting? What is happening to the subducted plate?What is happening to the subducted plate?

Convergent plate boundaries Features: 1) 1) 2) 2) 3) 3)

Convergent plate boundaries

Features: 1) …in ocean/ocean convergences 2) …in ocean/continent convergences 3) …in continent/continent convergences

Convergent plate boundaries Features: 1)Ocean trenches and volcanic island arcs 2)Benioff zone earthquakes, continental rim volcanoes and accretion 3)High plateaus, thrust faults and mountains

Transform plate boundary 2 plates slide past each other2 plates slide past each other Pacific Plate North American Plate

Transform Plate Boundaries The area where these plates meet is called a transform faultThe area where these plates meet is called a transform fault The San Andreas Fault in California is possibly the most famousThe San Andreas Fault in California is possibly the most famous

Transform Plates

Point Reyes, California

Transform plate boundaries Features: 1) 1) 2) 2) 3) 3)

Transform plate boundaries Features: 1) Major earthquakes 2) Offset linear features 3)Fracture zones

What kind of boundary? 12345

What features do they make? 12345

Plate Boundary Types

Why do the plates move? 1) 2) 3)

Why do the plates move? 1)Heat 2)Differences in density 3)Gravity

Why do the plates move? Inner core Outer core Mantle Crust Mantle and outer core are melted

Heat The Earth was originally molten The heat within the Earth is left over from then Radioactivity adds some heat

Density D=mass/volume Less dense floats on more dense If you heat an object or fluid, it expands, the density decreases A more dense fluid will force a less dense to rise

The average density of the Earth provides evidence of the relative densities of the different layers of Earth - crust, (lithosphere) -mantle (asthenosphere) and -core.

The average density of the Earth provides evidence of the relative densities of the different layers of Earth - crust, (lithosphere) -mantle (asthenosphere) and -core. The whole Earth is more dense than the rocks we see

Density Mantle is more dense than crust Oceanic crust is more dense than continental crust

Gravity g=Gm 1 m 2 /d 2 If anybody cares. What we do care about is that a) if you heat a fluid, its density decreases, b) the cooler fluid is more dense, so it sinks.

All together-- Convection happens!

Why do the plates move?

Convection happens!

The accepted mechanism for plate motion is: convection in the asthenosphere. Convection happens!

This plate is pulled this way…

Convection happens! …and this plate is pulled this way.

Wegener’s Evidence Wegener supported his hypothesis of continental drift with evidence from the puzzle fit of the continents, rock units, geologic structures, fossils and glacial evidence.

Evidence The modern theory of plate tectonics is supported by evidence from:

Evidence The modern theory of plate tectonics is supported by evidence from: A.paleomagnetism, B. C. D. a. b. c. Seafloor crust shows the direction of the magnetic field when the crust was formed

Evidence The modern theory of plate tectonics is supported by evidence from: A.paleomagnetism, B.age of ocean floor sediments C. D. a. b. c. Seafloor crust is older farther from the mid-ocean ridge

Evidence The modern theory of plate tectonics is supported by evidence from: A.paleomagnetism, B.age of ocean floor sediments C.ocean floor topography D. a. b. c. You can see the ridge and the suture zone around it

Evidence The modern theory of plate tectonics is supported by evidence from: A.paleomagnetism, B.age of ocean floor sediments C.ocean floor topography D. Wegener's evidence. a. b. c. Wegener had none of the above. He had to do it the hard way

Evidence The modern theory of plate tectonics is supported by evidence from: A.paleomagnetism, B.age of ocean floor sediments C.ocean floor topography D. Wegener's evidence. a.fossils b. c. Tropical fossils show up in polar regions

Evidence The modern theory of plate tectonics is supported by evidence from: A.paleomagnetism, B.age of ocean floor sediments C.ocean floor topography D. Wegener's evidence. a.fossils, b.jigsaw continents, c. They fit together pretty well

Evidence The modern theory of plate tectonics is supported by evidence from: A.paleomagnetism, B.age of ocean floor sediments C.ocean floor topography D. Wegener's evidence. a.fossils, b.jigsaw continents, c.rock types Similar rocks show up on different continents