29Evidence for Plate Tectonics Ocean DrillingThe data on the ages of seafloor sediment confirmed what the seafloor spreading hypothesis predicted.The youngest oceanic crust is at the ridge crest, and the oldest oceanic crust is at the continental margins.
30Which graph best represents the geologic age of the surface bedrock on the ocean bottom?
31Mid-ocean ridges (rifts) normally form where tectonic plates are (1) converging (3) stationary(2) diverging (4) sliding past each otherThe motion of the convection currents in the mantle beneath the Atlantic Ocean appears to be mainly making this ocean basin(1) deeper (3) wider(2) shallower (4) narrower
32If new crust is created at divergent boundaries, is earth getting larger? CONVERGENT BOUNDARIESOceanic crust - Oceanic Crustolder, denser crust subducts forming ocean trenchOceanic Crust – Continental Crustdenser oceanic crust subducts forming ocean trenchContinental Crust – Continental Crustresists subduction - folding, faulting, and mountain building
33Oceanic Crust – Oceanic Crust Older, denser oceanic crust is SUBDUCTEDVOLCANIC ISLAND ARC FORMED – ALEUTIAN ISLANDS
42More Evidence for Plate Tectonics Earthquake PatternsScientists found a close link between deep-focus earthquakes and ocean trenches.The absence of deep-focus earthquakes along the oceanic ridge system was shown to be consistent with the new theory.
43Convergent plate (subduction) boundaries have deeper earthquakes Divergent plate boundaries and collision zones have shallow earthquakes
45The greatest number of earthquakes in the cross section occurred at: Sea levelBetween sea level and a depth of l00 kms.3. at a depth between 100 – 300 kms.4. At a depth between 300 – 600 kms.
46Which cross section has arrows that best represent the relative motion of the crustal plates along the Wadati-Benioff zone beneath the Tonga Trench?
47TRANSFORM PLATE BOUNDARIES Transform Fault BoundariesTRANSFORM PLATE BOUNDARIESAt a transform fault boundary, plates grind past each other without creating or destroying the lithosphere.SHALLOW EARTHQUAKES Transform faults• Most join two segments of a mid-ocean ridge.• At the time of formation, they roughly parallel the direction of plate movement.
56So, what causes plates to move? Convection currents: drag and move the lithospheric plates above the asthenosphere(three sources of heat produce the convection currents):Leftover heat from earth’s formationDecay of Radioactive elementsPlate friction
58Convection Currents in the mantle drag and pull the lithospheric plates above them
593 types of plate boundaries caused by convection currents CASCADESMID-ATLANTIC RIDGETRENCH
60The arrows shown in the asthenosphere represent the inferred slow circulation of the plastic mantle by a processcalled(1) insolation (3) conduction(2) convection (4) radiation
61More Evidence for Plate Tectonics Hot SpotsA hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface; The Pacific plate moves over a hot spot, producing the Hawaiian Islands.Hot spot evidence supports that the plates move over the Earth’s surface.
62HOT SPOTSMajor regions of volcanic activity in the interior of plates away from plate boundaries.The cause of these hot spots is thought to be plumes of magma rising up from mantle producing sites of active volcanism.As the plate moves over a hot spot, a chain of volcanic mountains forms, like Hawaiian Islands
68This diagram provides evidence that the Pacific Crustal Plate was moving toward the(1) south (3) southwest(2) east (4) northwest
69SUMMARY OF P.T.: The plate tectonic model suggests: (1) continents can move across the surface of the globe(2) patterns of volcanism can change and shift across the globe as plates and their boundaries evolve and move(3) new oceans may grow(4) oceans basins close and are deformed to produce mountains