2. CONTINENTAL DRIFT AND PLATE TECTONICS

3. DRIFT AND PLATES Continental drift concept Introduction did continents originate at their present locations or did they move to where they are today? drift concept supplied information to aid in the formulation of rock plate or tectonic plate concept a solid lithosphere floating on top of the asthenosphere gives an idea of how plates can float Accretion of continental material took place

4. DRIFT AND PLATES convection cells in Earth’s interior is the force which split the lithosphere and are the driving force in continental separation

5. DRIFT AND PLATES Accretion of Continental Materials during Drift---Western USA

6. DRIFT AND PLATES who was the first to observe this map fit? Alfred Wegener was the first to publish a summary of ideas about continental drift in 1912. some ideas in the publication were: 1) the protocontinent or supercontinent was named Pangaea; 2) southern section was named Gondwana or Gondwanaland and northern section, Laurasia; 3) the protocontinent broke in pieces about 150- 200 million years ago

7. DRIFT AND PLATES Some important data confirming continental drift map fit--already mentioned mountain chains formed on continents with longitudinal axes perpendicular to movement of the continents--examples: Himalayan, Rocky Mountain and Andes Mountain chains same fossils (in rocks),same rocks, mountain ranges, and glacial features located on different continents in areas representing prejoined positions prior to continental drift

8. DRIFT AND PLATES Initial ideas of continental drift jig saw puzzle or map fit of continents

9. Matching of Fossils from Common Locations on Separated Continents

10. Matching of Mountain Chains from Common Locations on Separated Continents

11. Matching of Glacial Deposits from Common Locations on Separated Continents

12. DRIFT AND PLATES presence and shape of global ocean ridge a ridge is a raised region on ocean basin which is believed to represent prejoined or splitting area of separated continents--the shape of the ridge contours shape of coast lines of separated continents--- this is most evident in the mid Atlantic ocean

13. Global Ocean Ridge

14. DRIFT AND PLATES seafloor spreading age of rocks located on equivalent positions on both sides of the ridge are the same--rocks progressively increase in age away from the ridge magnetic intensities in the rocks are found to be the same on equivalent sides of the ridge--on both sides of ridge magnetic intensity alternates between normal(high intensity) and abnormal(low intensity)

15. DRIFT AND PLATES

16. Magnetic Intensities and Sea Floor Spreading

17. DRIFT AND PLATES Lithospheric plates and plate tectonics where are the spreading continents going? the answer was important in initiating the rock plate concept rock sections or plates which diverge from spreading zones move towards or converge on subduction zones Rock plates ocean basin and continental sections float in the asthenosphere, some plates diverge, some converge and some move parallel (to each other)

18. DRIFT AND PLATES Classification of rock plate boundaries volcanism and seismic activity are abundantly associated with plate boundaries boundaries are classified as divergent, convergent, or transformed boundaries divergent boundary--includes all ridges and rifts--tensional forces caused by convection cells drive the plates apart

19. DIVERGENT PLATE BOUNDARY

20. DRIFT AND PLATES kinds of divergent plate boundaries--1)ocean basin to ocean basin boundary; example is the mid ocean ridge

21. DRIFT AND PLATES 2) continental to continental boundary

22. DRIFT AND PLATES convergent boundaries--includes all subduction boundaries--compressional forces caused by convection cells drive plates towards each other--volcanic arcs are associated with convergent boundaries

23. Convergent Plate boundary

24. 3 types of convergent plate boundaries 1) Ocean basin to continental boundary (Example is the Cascade Mountain chain)

25. 2) Ocean basin to ocean basin boundary (Examples are Aleutian Islands and Japan)

26. Aleutian Islands and Japan

27. 3) Continental to continental plate boundary (Example is India and Asian continent boundary)

29. DRIFT AND PLATES transformed boundary--plates move parallel to boundary Example are those off the Coast of Western U.S.A.

30. DRIFT AND PLATES Major Plates on Earth and Movement Rates Movement rates are about as fast as your fingernails grow