1. CHAPTER 9 PLATE TECTONICS

4. Exploring the Ocean Floor Ocean Drilling & Mapping Ocean Drilling & Mapping The Glomar ChallengerThe Glomar Challenger SONAR – Sound Navigation and RangingSONAR – Sound Navigation and Ranging mapping ocean floor mapping ocean floor

5. Exploring the Ocean Floor Ocean Mapping Revealed: Ocean Mapping Revealed:  Deep-Ocean Trenches Long curved valleys along the edges of some ocean basinsLong curved valleys along the edges of some ocean basins Marianas Trench – 11 kilometers deepMarianas Trench – 11 kilometers deep

6. Exploring the Ocean Floor Ocean Mapping Revealed: Ocean Mapping Revealed:  Mid-Ocean Ridges A long chain of mountains extending the length of the oceanA long chain of mountains extending the length of the ocean Extends for 70,000 kmExtends for 70,000 km Through all major oceansThrough all major oceans

7. Exploring the Ocean Floor Ocean Mapping Revealed: Ocean Mapping Revealed:  Seamounts & Seamount chains Underwater volcanoes Underwater volcanoes Found through all the major oceans Found through all the major oceans

8. Composition of the Ocean Floor Age of Ocean Floor Age of Ocean Floor Igneous Rock – Basaltic composition Igneous Rock – Basaltic composition Same type of rock found in the Earth’s mantleSame type of rock found in the Earth’s mantle Ocean floor Youngest near the ocean ridges and Oldest at continental shelves, farthest from the ridges.Ocean floor Youngest near the ocean ridges and Oldest at continental shelves, farthest from the ridges. Oceans are geologically young Oceans are geologically young No ocean floor is older than 180 million years old.No ocean floor is older than 180 million years old. Pillow basalts on the South Pacific seafloor

9. The Process of Sea-Floor Spreading Harry Hess – Geologist Harry Hess – Geologist New ocean-floor forms at mid-ocean ridges New ocean-floor forms at mid-ocean ridges Slowly moves outward across ocean basinsSlowly moves outward across ocean basins Ocean floor gets wider Ocean floor gets wider Sinks into mantle beneath Deep-Ocean TrenchesSinks into mantle beneath Deep-Ocean Trenches

10. Process of Sea-Floor Spreading Magma Erupts Along Mid-Ocean Ridges Magma Erupts Along Mid-Ocean Ridges Magma cools to form new ocean floorMagma cools to form new ocean floor Slowly moves outward across ocean basins Slowly moves outward across ocean basins New floor is added and older floor moves outwardNew floor is added and older floor moves outward Ocean floor gets widerOcean floor gets wider Subduction at Deep-Ocean Trenches Subduction at Deep-Ocean Trenches Older ocean floor returns (sinks) to mantle at deep ocean trenchesOlder ocean floor returns (sinks) to mantle at deep ocean trenches

11. for Sea-Floor Spreading

12. PALEOMAGNETISM & The Earth’s Magnetic Field MAGNETIC STRIPES

13. THE EARTH’S MAGNETIC FIELD Background

14. The earth behaves like a bar magnet North magnetic pole South magnetic pole

15. North magnetic pole South magnetic pole magnetic lines of force

16. Earth’s magnetic field has TWO poles It is DIPOLAR

17. PALEOMAGNETISM MAGNETIC STRIPES

18. PLATE TECTONIC EVIDENCE Magnetic Stripes PALEOMAGNETISM Paleomagnetism Paleomagnetism Ancient Fossil Magnetism preserved in rocksAncient Fossil Magnetism preserved in rocks  Magnetism “Curie Point” - temperature of cooling magma when iron-rich minerals become magnetized“Curie Point” - temperature of cooling magma when iron-rich minerals become magnetized cools below 768C (1414F) cools below 768C (1414F)  The Rock Magnetite - Iron-rich mineralMagnetite - Iron-rich mineral abundant in molten basalt magma abundant in molten basalt magma

19. MAGNETIC REVERSALS Magnetic Domains in rock align with Earth’s current magnetic field lines Magnetic Domains in rock align with Earth’s current magnetic field lines Once molten rock (magma) cools, magnetic pole alignment is “frozen” in positionOnce molten rock (magma) cools, magnetic pole alignment is “frozen” in position Normal PolarityNormal Polarity same as today’s M.F. same as today’s M.F. (magnetic field) (magnetic field) Reverse PolarityReverse Polarity opposite of today’s M.F. opposite of today’s M.F. Measured with a “Magnetometer” Measured with a “Magnetometer”

20. MAGNETIC REVERSALS Magnetic field reversals revealed in stripes Magnetic field reversals revealed in stripes Recorded in sea-floor rocksRecorded in sea-floor rocks Confirms seafloor spreadingConfirms seafloor spreading A Period of Normal Magnetism B Period of Reverse Magnetism C Period of Normal Magnetism

21. Earthquake Patterns Associated w/plate boundaries Deep-focus earthquakes along trenches Provide a method for tracking the subducting plates Deep-focus earthquakes along trenches Provide a method for tracking the subducting plates The deeper the EQ, the farther it is from the subduction zone and beneath the over riding plate Red – deep Yellow – medium Blue – Shallow

22. OCEAN FLOOR AGE Youngest Ocean floor Youngest Ocean floor near ocean ridgesnear ocean ridges Older floor farthest from ridgesOlder floor farthest from ridges Oldest Ocean floor Oldest Ocean floor Near subduction zones at deep-ocean trenches Near subduction zones at deep-ocean trenches about 180 million yrs. old about 180 million yrs. old

23. Motion and Direction of Plates Hot Spots Indicate Movement and Direction of plates Indicate Movement and Direction of plates Rising plumes of molten materialRising plumes of molten material Volcanoes form over plumesVolcanoes form over plumes

24. Motion & Direction of Plates Hawaiian Island Chain Hawaiian Island Chain Island Chains indicates/mark plate movementIsland Chains indicates/mark plate movement 70 MY; 6,000 miles long 70 MY; 6,000 miles long

25. Motion & Direction of Plates 6,000km - Hawaiian Ridge-Emperor Seamount chain 6,000km - Hawaiian Ridge-Emperor Seamount chain A record of the plate’s direction of motionA record of the plate’s direction of motion Sharp bend in the chain indicates how the motion of the Pacific Plate abruptly changed about 43 million years ago. Sharp bend in the chain indicates how the motion of the Pacific Plate abruptly changed about 43 million years ago. Why the Pacific Plate changed direction is not known. Why the Pacific Plate changed direction is not known. May be related to the collision of India into the Asian continent.May be related to the collision of India into the Asian continent. Plate changed direction about 43-45 mya

26. Motion & Direction of Plates How fast are plates moving? How fast are plates moving? The Arctic Ridge has the slowest movement a less than The Arctic Ridge has the slowest movement a less than 2.5 cm/yr 2.5 cm/yr Arctic Ridge

27. Motion & Direction of Plates How fast are plates moving? How fast are plates moving? East Pacific Rise (near Easter Island, in the So. Pacific about 3,400 km west of Chile) has the fastest rate of movement at more than 15 cm/yr.East Pacific Rise (near Easter Island, in the So. Pacific about 3,400 km west of Chile) has the fastest rate of movement at more than 15 cm/yr.