Chapter+2+-+Plate+Tectonics

Chapter+2+-+Plate+Tectonics - Grotzinger • Jordan...

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Unformatted text preview: Grotzinger • Jordan Understanding Earth Sixth Edition Chapter 2: PLATE TECTONICS: The Unifying Theory © 2011 by W. H. Freeman and Company Chapter 2: Chapter Plate Plate Tectonics: Tectonics: The Unifying The Theory Theory About Plate Tectonics About • It is the movement of plates and the It forces acting on them. forces • It explains the distribution of volcanoes, It earthquakes, folded mountain chains, rock assemblages, and seafloor structures. • The forces that drive plate motions arise The from the mantle convection system. from Lecture Outline Lecture 6. Theory of plate tectonics and the 6. scientific method scientific 1. Evolution of the Theory 1. Continental drift: “jjig-saw ig-saw puzzle” fit of continents 1. Evolution of the Theory 1. Continental Continental drift: drift: similarity of rock similarity assemblages and ages across oceans oceans 1. Evolution of the Theory 1. Continental Continental drift: drift: distribution of distribution certain fossils 1. Evolution of the Theory 1. Seafloor Seafloor spreading: spreading: geological geological activity in midactivity ocean ridges ocean 1. Evolution of the Theory 1. Seafloor Seafloor spreading: spreading: new crust new formed there formed Thought questions for this chapter Thought What mistakes did Wegener make in formulating his What theory of continental drift? Do you think the geologists of his era were justified in rejecting his theory? his He assumed that some external force (tides or winds) led He to movement of the continents but remember geologists in that era didn’t know about mantle convection in 2. The Mosaic of Earth’s Crustal Plates 2. ● divergent, convergent, transform divergent, 2. The Mosaic of Earth’s Crustal Plates 2. ● next: a detailed look at the above next: Thought questions for this chapter Thought Why are there active volcanoes along the Pacific coast in Why Washington and Oregon but not along the east coast of the United States? The pacific coasts is located along a plate boundary, the east coast is not plate How do the differences between continental and oceanic How crust affect the way lithospheric plates interact? crust Some plates are getting larger while others are getting Some smaller smaller 3. Rates and History of Plate Motion 3. Ship towing a Ship sensitive magnetometer sensitive Mid-Atlantic Ridge high intensity low intensity lo Magnetic Magnetic anomalies: anomalies: seafloor areas seafloor of high and low magnetic values 3. Rates and History of Plate Motion ● magnetic time scale developed magnetic 3. Rates and History of Plate Motion 3. Figure 2.15 ● magnetic isochrons on the seafloor magnetic 3. Rates and History of Plate Motion 3. ● Velocity = 60 km / 3.3 mil. yr. = 18 km / mil. yr. (or 18 mm / yr) 18 3. Rates and History of Plate Motion 3. Example relative plate velocities: East Pacific Rise (Pacific and Nazca plates) – East 138 to 150 mm/yr 138 South Atlantic (Mid-Atlantic Ridge) – South 34 to 35 mm/yr 34 Southern Ocean, south of Australia – Southern 70 to 75 mm/yr 70 Southern Ocean, south of Africa – Southern 14 mm/yr 14 Thought questions for this chapter Thought In Figure 2.15, the isochrons are symmetrically distributed In in the Atlantic Ocean, but not in the Pacific Ocean. For example, seafloor as much as 180 million years old (in darkest blue) is found in the western Pacific, but not in the eastern Pacific. Why? There is seafloor speading in the Atlantic Ocean as it is caused by rifting along the North American – Eurasian plates. The Pacific Ocean is “ringed by a plate boundary” and consists mostly of the Pacific Plate. and 5. Mantle Convection: The Engine 5. of Plate Tectonics of Upper Upper mantle Theory 1: Theory whole mantle convection convection Plate recycling extends to the core­ mantle boundary. 700 km Lower mantle 2900 km Outer core 5. Mantle Convection: The Engine 5. of Plate Tectonics of Theory 2: Theory stratified convection convection The lower mantle convects more sluggishly than the upper mantle. Boundary near Boundary near 700 km separates the two different convection systems. 5. Mantle Convection: The Engine of Plate Tectonics of spreading spreading centers and hot spots spots 6. Theory of Plate Tectonics and the Scientific Method Scientific • Plate tectonics is not a dogma, but a confirmed theory Plate whose strength lies in its simplicity, its generality, and its consistency with many types of observations. its • This theory has survived so many attempts to prove it This wrong and has been so important in explaining and predicting so many phenomena that geologists treat the theory as fact. the • Reasons why proof and acceptance took so long: very Reasons cautious approach of many scientists studying this issue; global scale of the problem; and specialized technology required to gain data took time to develop. technology Thought questions for this chapter Thought Would you characterize plate tectonics as a hypothesis, a Would theory, or a fact? Why? theory, The theory of plate tectonics was not widely accepted The until the banded patterns of magnetization on the ocean floor were discovered. In light of earlier observations – the jigsaw-puzzle fit of the continents, the occurrence of fossils of the same life-forms on both sides of the Atlantic, and the reconstruction of ancient climate conditions – why are these banded patterns of magnetism such key pieces of evidence? pieces Key terms and concepts Continental drift Continental Covergent boundary Divergent boundary Island arc Isochron Magnetic anomaly Magnetic time scale Mantle plume Mid-ocean ridge Pangaea Plate tectonics Relative plate velocity Key terms and concepts Seafloor spreading Seafloor Spreading center Subduction Transform fault ...
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This note was uploaded on 07/12/2011 for the course EAS 2600 taught by Professor Ingalls during the Summer '08 term at Georgia Institute of Technology.

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