Theory of Plate Tectonics

Transcription

1 Plate Tectonics

2 Theory of Plate Tectonics Lithosphere is made of sections called plates that move around called continental drift Plates move because they float on the asthenosphere Most plates consist of ocean and continental crust 2 ocean plates: Nazca and Philippine

3 Theory of Plate Tectonics Cont. Supercontinents: one large landmass of all continents. Happened 3x. Last called Pangea Ref Table p9 Plates fit together like puzzle pieces Similar fossils are found on many continents. Example: Glossopteris Mountain ranges match as far as rock structure, age, shape and position

4 Plate Boundaries Divergent Boundary: plates move apart magma rises creating new land by intrusions and extrusions. Also called sea floor spreading Produces shallow earthquakes On a continental crust, a rift valley will form with mountains created by faulting and volcanic activity

5 Plate Boundaries Cont. In the ocean crust, a mid-ocean ridge forms from faulting and volcanic activity - a mountain range with a rift valley on the ocean floor Result: Older rock is near the continents Symbol:

6 Plate Boundaries Cont In the ocean crust, a mid-ocean ridge forms from faulting and volcanic activity - a mountain range with a rift valley on the ocean floor Symbol:

7 Plate Boundaries Cont. Convergent boundaries: 3 types: oceanocean, ocean-continent, continent-continent In ocean-ocean and ocean-continent the crust comes together and the denser plate sinks under the other called subduction Subduction results in ocean trenches and volcanic islands formed Earthquake activity along the subducting plate Contact and regional metamorphism occur

8 Plate Boundaries Cont. Young mountains: ocean-continent will produce mountains on the overriding plate as friction from the subducting plate causes the rock in the overriding plate to melt. Ex. Cascades in Oregon, Washington Mountain building is called orogeny In continent-continent, the crust is pushed upwards creating the highest mountains - Himalayas Symbol:

9 Convergent Boundary

10 Plate Boundaries Cont. Transform Boundary: plates slide past each other Rocks sliding past each other catch building energy. When released earthquakes occur Symbol:

11 Transform Boundary

12 Driving Force of Plate Tectonics Mantle convection pushes plates apart at divergent boundaries Energy for convection comes from: heat from earth s interior causes less dense melted rock to rise, gravity pulls down cooler rock

13 Hot Spots Volcanic activity in the center of plates Examples: Hawaii, Yellowstone National Park, Adirondack Mountains NY Rising magma remains stationary and as the plate moves the magma rises in different spots Regions of intrusive and extrusive activity

14 Hot Spot - Hawaii

15 Effect of Plate Tectonics Continents appear to be puzzle pieces because of the breakup of Pangea Similar rocks, minerals, fossils, mountain ranges where the puzzle pieces fit together Variation in life forms comes from evolution Similar fossils on all continents of plants and animals could only happen if connected Plate movements have changed landmass locations

16 Effect of Plate Tectonics Cont. Basaltic igneous rock forms at the mid-ocean ridge so the older rock is the continents, younger rock is near the ridge Hottest rock is near the ridge Magnetic polarity: magnetic poles flip-flop. Reason unknown. Polarity is detected in the rocks on both sides of the ridge. Polarity is symmetrical Ref Table p5

17 Definition: vertical quake on the ocean floor that produces waves Cause: faulting along ocean floor Open ocean: waves are small Shallow water near shoreline: height up to 30m Speeds: 500km/hr Tsunami

18 Earthquakes and Volcanoes Earthquakes 101

19 Vocabulary Lithosphere: crust and upper mantle Strata or bed: Layers of sedimentary or extrusive igneous rock Deformed layers: no longer show original horizontality Folded: layers are curved or bent Faulted: layers are displaced(shifted) along a crack Tilted layers are slanted Uplifted: land and fossils are raised

20 Original Horizontality and Deformed Strata

21 Earthquakes Definition: a natural rapid shaking of the lithosphere caused by the release of stored energy in rock Caused: movement of rocks along faults, usually along the borders of continents and oceans Focus: origin of the earthquake where energy is given off in seismic waves

22 Earthquakes Cont. Epicenter: point on surface above the earthquake Instrument: seismograph - records the seismic waves

23 Earthquakes Cont. Earthquake waves: P wave: primary wave, travels in direction the waves are moving, travels through solid, liquid, gas S wave: secondary wave, travels at right angles to the direction of movement. Moves ONLY in SOLIDS L Waves: surface waves cause damage

24 Earthquakes Cont. Properties of waves: P waves are the fastest, S is the second fastest Velocity depends on material - The more dense, the greater the velocity Waves passing from one density to another are bent or refracted Pressure, velocity

25 Seismic Waves

26 Seismograph

27 Locate the Epicenter Use 3 seismograms: the distance to each epicenter is drawn as the radius of a circle. The point where the 3 meet is the epicenter Read the seismogram: read times for the S and P waves. The larger the time difference, the further away the quake is

28 Locate the Epicenter Cont. Subtract: S-P= time difference Ref Table p11 and scrap paper: mark scrap with the time difference. Place the 0 mark on the P line and slide in the graph until the Time mark touches the S line. Then look at the X axis and reach the epicenter distance

29 Locate the Epicenter Cont. Use the epicenter distance for each seismogram to draw a circle using the map scale. Epicenter is any place on the circle Epicenter: mark with an X the place where the 3 circles cross. Need 3 circles because 2 circles gives you 2 possible locations of the epicenter

30 Locate an Epicenter Cont. Find the P travel time for 5000 km How do you prove your epicenter is correct?

31 Seismic Belts 80% of earthquakes occur in the Ring of Fire in the Pacific Ocean 15% of quakes occur across Southern Europe and Asia

32 Crust and Interior Properties

33 Crust and Interior Properties Zones: 3 solid zones - crust, mantle, inner core 1 liquid zone - outer crust Crust: 2 types Continental - thicker and made of granite, felsic, low density, Al and Si Oceanic - thinner and made of basalt, mafic, high density, Mg and Fe

34 Crust and Interior Properties Cont. Mantle - greatest volume. Boundary between the crust and mantle is called the Moho Solid and plastic solid silly putty called the asthenosphere. Asthenosphere is where convection takes place moving the plates Core - Outer core is liquid Fe and Ni, inner core is solid Fe and Ni Density, temp, pressure, depth Ref Table p10

35 Magma and Volcanoes

36 Magma Definition magma: mixture of molten rock, suspended minerals and gases with temps of C pressure, temp at which rock melts Water in pores of rocks, temp at which rock melts Viscosity: how easily liquid rock will move

37 Magma Cont. Types of Magma - 3 types Basaltic magma - upper mantle rock melts, little dissolved gases, low viscosity (magma moves slowly), quiet eruption Andesitic magma - along continent edges where oceans subduct, 60% silica, medium viscosity Rhyolitic magma - silica mixed with water, large volume gas, high viscosity, explosive

38 Magma Types

39 Magma Cont. Intrusive activity: magma moves through cracks in rocks because it is less dense Extrusive activity - magma, now called lava, moves out onto the surface of earth

40 Intrusion and Extrusion

41 Volcanoes Definition volcanoes: mountain composed of extrusive igneous rock Hazards: falling rocks, building buried or burned by lava, volcanic ash mixed with water to form mudslides, gases such as S, Cl, or CO 2, volcanic ash blocking insolation Activity: measured by satellites, tilt meters and earthquake activity

42 Volcanoes Cont. Plateau: high, flat landscape composed of horizontal layers of lava 3 types of volcanoes Cinder cones: western US, steep sides, magma mixed with water, large amount gas, explosive Composite volcano: western US Cascades-rock fragments alternate with lava, large amount water, gas silica and gases, violently explosive Shield volcano: Hawaii, broad, gently sloping circular base, nonexplosive