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