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Chapter 3Plate Tectonics

Current Plate Boundaries and Relative MotionThe Early Case for Continental DriftSkepticism about Continental Drift

Paleomagnetism and the Revival of Continental Drift

Recent Evidence for Continental DriftHistory of Continental Positions

Plate Reconstructions

Fossil Evidence for Gondwana Permian-PennsylvanianEarly TriassicPermian

Distribution of Paleozoic Glaciers and Glacial StriationsEvidenceHypothesis

Polar Wander Hypothesis

Wegeners Reconstruction of Apparent South Polar Wander PathNB : that Wegener believed that the continents moved, not the pole !Polar Wander HypothesisFrom paleoclimatic evidence, Wegener found that the apparent position of the poles (and therefore equator) had moved through geological time.Possible interpretations:Continents were motionless and poles actually movedPoles were motionless and continents movedBoth occurred - most likely scenario

Wegeners Concept of Continental Drift and OrogenesisMost geologists and geophysicists rejected Wegeners ideasbecause they violated what was known about the strength of rocks.

Also, centrifugal force (from Earths rotation) along with tidal forceswere deemed to be too small to move the continents!

Paleomagnetism - Revival of Continental Drift

Apparent Geomagnetic Pole

Magnetic Polar Wander PathsBest interpretation is that there was a single magnetic pole and North America and Europe separated in the Late Triassic formingthe Atlantic Ocean basin

Goodness of Fit of the 100 m depth contourContinental ShelvesLithologicaland agecorrelationfor rockunitsGlacialstriaeSea-Floor SpreadingHesss Driving ForceExplanations

Plates and Plate Motion

Hess Heat Engine

Lithosphere vs. Asthenosphere

Passive UpwellingHow Do We Know that Plates Move?Marine Magnetic AnomaliesMagnetic Stripe Map

Another Test: Fracture Zones and Transform FaultsEuler Poles of Rotation

Measuring Plate Motion DirectlySpace GeodesyVLBIGPSDORIS

Marine Magnetic Anomalies

Magnetic Time Scale

Magnetic Stripe Formation at Ridge Crest

Age vs. Magnetic Polarization

Sea Floor Age MapGPS Global Velocity Field

Typical GPS Time Series and SCIGN Mount

Photo credit: http://www.scign.org/CGPS Site SCMSJPL Time Series for Yellowknife, CAPlates Move, it show a few plate boundary ?Convergence BoundaryBetween oceanic crust vs continental crust

Divergent BoundaryMid-oceanic Ridge

Transform Fault BoundaryOff-set between Mid-oceanic Ridge

Ocean - Continent Convergence

Divergent Boundary Earthquakes

Transform Boundary Earthquakes

Transforms vs. Fracture Zones

Convergent Margin EnvironmentThe Attractiveness of Plate TectonicsWhat Causes Plate Motions?Mantle Plumes and Hot SpotsRidge PushSlab PullThe Relationship Between Plate Tectonics and Ore Deposits

Ridge Push

Slab Pull

Trench Suction

Global Distribution of Putative Mantle Plumes or Hot Spots

Hawaiian Volcanics Age Progression

Hydrothermal Orogenesis and Divergent Plate Motion

Island Arc Orogenesis of Bedded Ore Deposits

Possible Relationship of Western US Ore Belts to Subduction Geometry