Post on 09-Mar-2018
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Environmental Geology – Plate tectonics
Plate tectonics
Reading: This week: Ch 3Next week: Ch 4
Internal processes:
Environmental Geology – Plate tectonics
The Earth’s magnet
Magnetic dip
• at equator: 0 (horizontal)
• at pole: 90 deg (vertical)
tells us about the latitude when the rooks cooled
Magnetic azimuth
• the compass needle points north
Normal polarity
Environmental Geology – Plate tectonics
The Earth’s magnet
Magnetic dip
• at equator: 0 (horizontal)
• at pole: 90 deg (vertical)
tells us about the latitude when the rooks cooled
Magnetic azimuth
• the compass needle points south
Reverse polarity
Environmental Geology – Plate tectonics
Reconstructing plate motion
Plate tectonics:
The magnetic tape recorder:
Given the oceanic record we can wind back the plates to see how the plates have been moving.
This shows us how Pangaea broke up.
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Environmental Geology – Plate tectonics
Continental magnetizationPlate tectonics:
Environmental Geology – Plate tectonics
Plate motion further back in timePlate tectonics:
Environmental Geology – Plate tectonics
The formation of PangaeaPlate tectonics:
When we add the continental plate motion recoded we can extend plate reconstruction back beyond 200Ma
i.e. prior to the break-up of Pangaea
QUESTION
Environmental Geology – Plate tectonics
Properties of geological materialsEarth’s interior:
How can plates move across the Earth’s surface?
The Earth is not a rigid solid, but a plastic solid.
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Environmental Geology – Plate tectonics
Properties of geological materialsEarth’s interior:
How can plates move across the Earth’s surface?
The Earth is not a rigid solid, but a plastic solid.
Brittle failure: Rupture
Plastic deformation: Ductile flow
Environmental Geology – Plate tectonics
An overviewEarth’s interior:
Environmental Geology – Plate tectonics
Categories of plate boundariesDivergent
• Established mid-ocean ridge• New rift zone, new ocean
Transform• Along mid-ocean ridges• Across continents
Convergent• Ocean – continent • Ocean – ocean • Continent – continent
Plate tectonics:
Environmental Geology – Plate tectonics
Categories of plate boundaries
Divergent• Established mid-ocean ridge Mid-Atlantic Ridge• New rift zone, new ocean East African Rift
Transform• Along mid-ocean ridges Fracture Zones e.g. south Pacific• Across continents San Andreas Fault
Convergent• Ocean – continent Off west coast of South America• Ocean – ocean Japan Trench, western Pacific• Continent – continent Himalaya
Plate tectonics:
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Environmental Geology – Plate tectonics
Mid-Atlantic RidgeDivergent boundaries:
Environmental Geology – Plate tectonics
Mid-ocean ridge resourcesDivergent boundaries:
Black smokers produce rich mineral deposits …at 2.5 km depth
Environmental Geology – Plate tectonics
The East African Rift and Red Sea
Divergent boundaries:
Environmental Geology – Plate tectonics
The Red SeaDivergent plate boundaries:
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Environmental Geology – Plate tectonics
The continental rifting process provides the right environment for oil formation within continental margin
sediments
Divergent plate boundaries:
Oil at the continental margin
Environmental Geology – Plate tectonics
Ocean transformsTransform plate boundaries:
Mid-ocean ridges are
offset by ocean
transforms:
Fracture Zones
Ocean bathymetry map
Environmental Geology – Plate tectonics
Ocean transformsTransform plate boundaries:
Environmental Geology – Plate tectonics
San Andreas FaultTransform plate boundary:
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Environmental Geology – Plate tectonics
San Andreas FaultTransform plate boundary:
Environmental Geology – Plate tectonics
Different typesConvergent plate boundaries:
Environmental Geology – Plate tectonics
South AmericaConvergent plate boundaries:
Environmental Geology – Plate tectonics
Different typesConvergent plate boundaries:
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Environmental Geology – Plate tectonics
India and Asia – the HimalayaConvergent plate boundaries:
QUESTION
Environmental Geology – Plate tectonics
The Ring of Fire
Refers to the concentration of earthquakes and volcanoes around the Pacific rim.
Environmental Geology – Plate tectonics
Determining plate velocitiesPlate tectonics:
1. Magnetic stripes on the ocean floor
2. Hotspot tracks record plate motion
Environmental Geology – Plate tectonics
Hotspot tracksPlate tectonics:
Strings of volcanic ocean islands recording the motion of the plate
Hawaiian chain The formation process
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Environmental Geology – Plate tectonics
Global hotspot tracksPlate tectonics:
Environmental Geology – Plate tectonics
Plate velocitiesPlate tectonics:
Environmental Geology – Plate tectonics
The unifying theoryPlate tectonics:
Plate tectonics: Recognizes that rigid plates are moving across the Earth’s surface.
A unifying theory: A single theory that explains a large body of evidence.
Other examples:
Physics – theory of relativityChemistry – nature of a chemical bondAstrophysics – the Big BangBiology – DNAGeology – plate tectonics