ESC 1000 Earth Science Name: __Answers___

Chapter 7:Plate Tectonics: A Scientific Theory Unfolds

(12^th Edition : Chapter 7 Typed By: Margarette Eugene)

(formerly Chapter 8 in the 11^th Edition)

Part K Chapter 7 Key Terms 30 Points

Fill in the blanks with the word or words that best fit the definition:

1. Asthenosphere- The subdivision of a mantle situated below the lithosphere. The zone of weak material exists below the depths of about 100 kilometers and in some region extends as deep as 700 kilometers. The rock within this zone is easily deformed.

2. Continental drift theory- A theory that originally proposed that the continents are rafted about. It has essentially been replaced by the plate tectonics theory

3. Continental volcanic arc- Mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent.

4. Convergent plate boundary- A boundary in which two plates move together, causing one of the slabs of lithosphere to be consumed into the mantle as it descends beneath on an overriding plate.

5. Curie Point- the temperature above which a material loses its magnetizations.

6. Deep-ocean trench- An elongated depression in the seafloor produced by bending of oceanic crust during subduction.

7. Divergent plate boundary- A region where the rigid plates are moving apart, typified by mid-oceanic ridges.

8. fossil magnetism- (also called paleomagnetisim) - The natural remnant magnetism in rock bodies. The permanent magnetization acquired by rock that can be used to determine the location of the magnetic poles and latitude of the rock at the time is became magnetized.

9. Fracture – Any break or rapture in rock along with no appreciable movement has taken place.

10. Hot spot- A concentration of heat in a mantle capable of producing magma, which turn extrudes onto the earth surface. The intraplate volcanism that produced the Hawaiian Islands is one example.

11. Island arc- A chain of volcanic islands generally located a few hundred kilometers from a trench where active subduction of one oceanic slab beneath another occurring. (same as Volcanic Island arc)

12. Lithosphere- The rigid outer layer of earth, including the crust and upper mantle.

13. Magnetic time scale- Time scale of the Earth’s Magnetic Field in recent past developed by establishing the magnetic polarity for lava flows of known age.

14. Mantle plume- A mass of hotter –than- normal mantle material that ascends towards the surface, where it may lead to igneous activity. These plumes of slid yet mobile material may originate as deep as the core-mantle boundary.

15. Normal polarity- A magnetic field that is the same as that which exists at present.

16. Ocean ridge system- A continuous elevation zone on the floor of all the major ocean basin and varying in width from 500 to 5000 kilometers (300 to 3000 miles). The rift at the crests of ridges represent divergent plate boundaries

17. Paleomagnetism- The natural remnant magnetism in rock bodies. The permanent magnetization acquired by rock that can be used to determine the location of the magnetic poles and latitude of the rock at the time is became magnetized.

18. Pangaea- The proposed supercontinent that 200 million years ago begin to break apart and form the present landmasses.

19. Partial melting – the process by which most igneous rocks melt. Since different minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a high silica content result.

20. Plate- One of numerous rigid sections of the lithosphere that moves as unit over the material of the Asthenosphere.

21. Plate tectonics- The theory that proposes the earth outer shell consists of individual plats that interact in varies ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself.

22. Reverse polarity- A magnetic field opposite to that which exists at present.

23. Ridge push- A mechanism that may contributes to plate motion. It involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity.

24. Rift (rift valley)- Along the axis of some oceanic ridge segments is a deep downfaulted structure.

25. Seafloor is spreading- The process of producing new seafloor between two diverging plats.

26. Slab pull- A mechanism that may contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and “pulls” the trailing lithosphere along.

27. slab suction – Another driving force which arises from the drag of a subducting slab on the adjacent mantle which results in an induced mantle circulation that pulls both the subducting and overriding plates toward the trench

28. Subduction zone- A long, narrow zone where one lithosphere plate descends beneath another.

29. Transform fault boundary- A boundary in which two plates slide past one another without creating or destroying lithosphere.

30. Volcanic island arc- A chain of volcanic islands generally located a few hundred kilometers from a trench where active subduction of one oceanic slab beneath another occurring.