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Plate Tectonics
Theory of Plate Tectonics
Lithosphere is made of sections called plates that move around called continental driftPlates move because they float on the asthenosphereMost plates consist of ocean and continental crust2 ocean plates: Nazca and Philippine
Theory of Plate Tectonics Cont.
Supercontinents: one large landmass of all continents. Happened 3x. Last called Pangea Ref Table p9Plates fit together like puzzle piecesSimilar fossils are found on many continents. Example: GlossopterisMountain ranges match as far as rock structure, age, shape and position
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
Plate Boundaries Cont.
– In the ocean crust, a mid-ocean ridgeforms from faulting and volcanic activity - a mountain range with a rift valley on the ocean floor
– Result: Older rock is near the continents– Symbol:
Plate Boundaries Cont
– In the ocean crust, a mid-ocean ridgeforms from faulting and volcanic activity - a mountain range with a rift valley on the ocean floor
– Symbol:
Plate Boundaries Cont.
Convergent boundaries: 3 types: ocean-ocean, 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
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:
Convergent Boundary
Plate Boundaries Cont.
Transform Boundary: plates slide past each otherRocks sliding past each other catch building energy. When released earthquakes occurSymbol:
Transform Boundary
Driving Force of Plate Tectonics
Mantle convection pushes plates apart at divergent boundariesEnergy for convection comes from: heat from earth’s interior causes less dense melted rock to rise, gravity pulls down cooler rock
Hot Spots
Volcanic activity in the center of platesExamples: Hawaii, Yellowstone National Park, Adirondack Mountains NYRising magma remains stationary and as the plate moves the magma rises in different spotsRegions of intrusive and extrusive activity
Hot Spot - Hawaii
Effect of Plate Tectonics
Continents appear to be puzzle pieces because of the breakup of PangeaSimilar rocks, minerals, fossils, mountain ranges where the puzzle pieces fit togetherVariation in life forms comes from evolutionSimilar fossils on all continents of plants and animals could only happen if connectedPlate movements have changed landmass locations
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 ridgeHottest rock is near the ridgeMagnetic polarity: magnetic poles flip-flop. Reason unknown. Polarity is detected in the rocks on both sides of the ridge. Polarity is symmetricalRef Table p5
TsunamiDefinition: 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
Earthquakes and Volcanoes
Earthquakes 101
VocabularyLithosphere: crust and upper mantleStrata or bed: Layers of sedimentary or extrusive igneous rockDeformed layers: no longer show original horizontalityFolded: layers are curved or bentFaulted: layers are displaced(shifted) along a crackTilted layers are slantedUplifted: land and fossils are raised
Original Horizontality and Deformed Strata
Earthquakes
Definition: a natural rapid shaking of the lithosphere caused by the release of stored energy in rockCaused: movement of rocks along faults, usually along the borders of continents and oceansFocus: origin of the earthquake where energy is given off in seismic waves
Earthquakes Cont.
Epicenter: point on surface above the earthquakeInstrument: seismograph -records the seismic waves
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
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
Seismic Waves
Seismograph
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 epicenterRead the seismogram: read times for the S and P waves. The larger the time difference, the further away the quake is
Locate the Epicenter Cont.
Subtract: S-P= time differenceRef 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
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 circleEpicenter: 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
Locate an Epicenter Cont.
Find the P travel time for 5000 kmHow do you prove your epicenter is correct?
Seismic Belts
80% of earthquakes occur in the “Ring of Fire” in the Pacific Ocean15% of quakes occur across Southern Europe and Asia
Crust and Interior Properties
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
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 platesCore - Outer core is liquid Fe and Ni, inner core is solid Fe and NiDensity, temp, pressure , depth Ref Table p10
Magma and Volcanoes
Magma
Definition magma: mixture of molten rock, suspended minerals and gases with temps of 800-1200°C
pressure, temp at which rock meltsWater in pores of rocks, temp at which rock meltsViscosity: how easily liquid rock will move
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
Magma Types
Magma Cont.
Intrusive activity: magma moves through cracks in rocks because it is less denseExtrusive activity - magma, now called lava, moves out onto the surface of earth
Intrusion and Extrusion
Volcanoes
Definition volcanoes: mountain composed of extrusive igneous rockHazards: falling rocks, building buried or burned by lava, volcanic ash mixed with water to form mudslides, gases such as S, Cl, or CO2, volcanic ash blocking insolationActivity: measured by satellites, tilt meters and earthquake activity
Volcanoes Cont.
Plateau: high, flat landscape composed of horizontal layers of lava3 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