CHAPTER 2 Plate Tectonics and the Ocean Floor (I) Instructor: Dr. Dong at ECC

Layered Earth Fig. 1.14

Fig. 1.15

Asthenosphere Upper mantle Plastic—deforms by flowing High viscosity—flows slowly

Plate tectonics explains: Global distribution of Volcanoes Earthquakes Faults Mountain belts Features of seafloor Evolution of continents and oceans

Exe. 2-1 How many layers in the earth structure? 2. What is the plate tectonic?

Hypothesis: Continental drift Wegener proposed one large continent (1912) Pangaea Surrounded by single large ocean Panthalassa About 200 million years ago

Fig. 2.2

Evidence for continental drift Puzzle-like fit of continents Edward Bullard fit continents at 2000m water depth Fig. 2.3

Evidence for continental drift Matching sequences of rocks and mountain chains Similar age, rock types, structures

Figure 2.4a

Figure 2.4b

Evidence for continental drift Glacial ages and other climate evidence Ancient glaciation in modern tropical regions Direction of glacial flow Distribution of organisms Same land animals distributed in different continents (e.g., South America and Africa)

Fig. 2.5

Fig. 2.6

Objections to continental drift Continents cannot “plow” through ocean crust Gravitational forces associated with tides too small

Exe. 2-2 List evidences to support the continental drift Why was the continental drift a hypothesis?

Evidence for plate tectonics Earth’s magnetic field Paleomagnetism Magnetic alignment (N or S) Magnetic inclination (magnetic dip) Latitude

Fig. 2.7

Apparent polar wandering Pangaea Fig. 2.8

Magnetic polarity reversals Fig. 2.9

How is earth’s magnetic field used for the tectonic plate? Exe. 02-03 How is earth’s magnetic field used for the tectonic plate?

Sea floor spreading Harry Hess (1962) Mid-ocean ridge site of new ocean crust Oceanic trench site of crust destruction (subduction) Fig. 2.10

Evidence to support sea floor spreading

Earth’s magnetic polarity as sea floor created 1. Parallel magnetic anomalies record changes in Earth’s magnetic polarity as sea floor created Fig. 2.11

2. Age of ocean floor increases away from crest of mid-ocean ridge Fig. 2.12

3. Global distribution of earthquakes Fig. 2.13

Evidence to support sea floor spreading Parallel magnetic anomalies record changes in Earth’s magnetic polarity as sea floor created Age of ocean floor increases away from crest of mid-ocean ridge Most large earthquakes occur along plate margins

Fig. 2.10

Plate tectonics theory Lithospheric plates “float” on the asthenosphere Large scale geologic features occur at plate boundaries Two major tectonic forces Slab pull Slab suction

Exe. 02-04 List evidences to support plate tectonic theory.