Plate Tectonics. A Major Revolution in Our Understanding of the Earth

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Darlene Hall
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1 Plate Tectonics A Major Revolution in Our Understanding of the Earth

2 There are fossils of marine organisms that can be found in many of the highest elevations of the world including the Himalayas

3 How did rocks that formed on the deep ocean floor near the equator end up making hills in San Francisco? Radiolarian chert in San Francisco If deposited by a great flood why are the beds so deformed?

4 North Eastern Japan March 11 th 2011

8 What is so great about the Theory Plate Tectonics? Why is it even important?

9 Volcano Global Distribution This map does not including all the volcanic activity along the MOR s

10 Global Distribution of Earthquake Occurrence For the most part, earthquakes occur along plate boundaries.

11 What are the Plate Boundary Types? Name a location that you could find each type. Is volcanism associated with the plate boundary and if so what type of volcanism? Which types of plate boundaries do you think create large earthquakes? How about tsunamis?

13 Divergent Plate Boundary * Practice drawing and labeling this picture---you need to know this by memory! e.g. Mid-Atlantic Ridge

14 Turkey Transform Plate Boundaries is a strike-slip fault plate boundary. The San Andreas Fault is an example (that is where we live!).

15 Oceanic to Oceanic Convergent Boundary * Practice drawing and labeling this picture---you need to know this by memory! e.g. Japan, Philippines, Indonesia, Aleutian Islands

16 Continent to Ocean Convergent Boundary Practice drawing and labeling this picture---you need to know this by memory! * e.g. N. California, Oregon, and Washington, Central and Western S. America

17 Continent to Continent Convergent Boundary Practice drawing and labeling this picture--- you need to know this by memory! India China

18 Cratons are very old, stable continental interiors. Often crystalline metamorphic rock. Cratons are composed of shields and platforms. A platform is sedimentary deposits covering the crystalline basement rocks of a shield.

19 *An important concept: Temperature change of an object changes the density of that object. Density differences controlled by temperature changes is what creates convection. Composition Felsic vs. Mafic Motion in the asthenosphere is what drives plate tectonics!

21 Pangaea Breakup

24 Building the Western Margin of North America Continents can grow by accretion of terranes. Much of Western North America is accreted terranes.

Islands and seamounts are created by the

carried away by the moving tectonic plate.

25 Emperor Seamounts Hawaiian Island are created by a Hot Spot. This is volcanism not associated with tectonic plate boundaries. Islands and seamounts are created by the volcanism over the hot spot but they are carried away by the moving tectonic plate. They are traveling towards a subduction zone where they will either be subducted or accreted.

27 Terrane Formation

29 Siberian Traps: A massive flood basalt event that is thought to have caused the largest mass extinction ever to occur. This mass extinction marks the Permian-Triassic boundary.

30 Photo by John Stodder; Image from Woods Hole Oceanographic Institution. Flood Basalt Coincident with the K-T mass extinction 65 Ma Cretaceous-Tertiary Boundary (End of the Dinosaurs!)

31 9 Ma Continents can grow from volcanism.

32 From the info given so far, what two ways do continents grow?

33 Oceanic to Oceanic Convergent Boundary * Practice drawing and labeling this picture---you need to know this by memory! e.g. Japan, Philippines, Indonesia, Aleutian Islands

34 Volcanic Island Arc

eruption, and alerted the Alaska Volcano

35 Ash plume arising from Mount Cleveland on May 23, 2006, as seen from the International Space Station. Astronauts were the first to realize the eruption, and alerted the Alaska Volcano Observatory to it. Cleveland Volcano Aleutian Islands Alaska

36 Alaska Aleutian Islands Trench

37 Japan Trench

38 Trench Indonesia

39 Micronesia and Melanesia (South Pacific) Trench Australia

40 Continent to Ocean Convergent Boundary Practice drawing and labeling this picture---you need to know this by memory! * e.g. N. California, Oregon, and Washington, Central and Western S. America

42 Continental Volcanic Arc

43 Large red triangles show volcanoes with known or inferred Holocene eruptions; small red triangles mark volcanoes with possible, but uncertain Holocene eruptions or Pleistocene volcanoes with major thermal activity. Yellow triangles distinguish volcanoes of other regions.

45 Central America and West Coast of South America Trench

46 Subduction (a closer look)

47 Tsunami

49 Discussion: What is the difference between an accreted terrane and a accretionary wedge? What is the ultimate cause of convection? What type of plate boundary do we live on?

50 Why did Pangaea break up? What are some of the consequences of this break up?

53 Continental Rifting

Passive Margin Example: East Coast of North

59 Passive Margin Example: East Coast of North America Sometimes called an Atlantic Style continental margin. Note: The edge of a continent is not necessarily a plate boundary. Notice that the North American Plate extends out into the Atlantic ocean to the spreading center.

61 Ophiolite Sequence: They can be scraped off pieces of ocean crust have been accreted to continents (accreted terrane). Ocean Crust comparison to the scale of the Grand Canyon.

65 Serpentinite Mt Diablo

69 Vulcan Octopus Rod Mickens / AMNH Pogonophora (Tube Worms)

71 Pillow Basalt

77 Divergent Plate Boundary * Practice drawing and labeling this picture---you need to know this by memory! e.g. Mid-Atlantic Ridge

78 Turkey Transform Plate Boundaries is a strike-slip fault plate boundary. The San Andreas Fault is an example.

80 WHAT KIND OF CONTINENTAL MARGIN DO WE LIVE ON?

84 Cross-section line through the East Bay Hills, the Bay, San Francisco and out the shelf to the Farallon Islands

85 Home Sweet Home The Cascade Range is a continental volcanic arc. Subduction of oceanic plate is occurring in the Pacific Northwest. Subduction ceased in Central and Southern California when the Farallon Plate completely subducted, thus we do not have active volcanism (related to subduction) in Central and Southern California.

87 Continent to Continent Convergent Boundary Practice drawing and labeling this picture--- you need to know this by memory! India China

88 Continental Continental Convergence 2011 Pearson Education, Inc.

89 Suture Zone

90 Continuity of mountain ranges and rock types Mountains of similar age and structure show continuity when continents are joined. This also suggests the same mountain building event. The collision of continents builds mountains!

91 Continent to Continent Convergent Plate Boundary A real mash up since continents do not want to subduct. They both are low density and want to float. India is still moving North and the Himalayas are still rising!

92 We start again in 10 minutes and 32 seconds. The coordinates of San Francisco is roughly: North 37 degrees, West 122 degrees If you wanted a more precise location, you would need to measure the angle in minutes. An even more precise measurement would include seconds. One degree=60 minutes One minute=60 seconds

93 Break time! A jellyfish does not have a brain or central nervous system, and they do not have specialized digestive, osmoregulatory, respiratory, or circulatory systems. ~90% water They control movement with a hydrostatic skeleton and many can sense light.

94 Intro to Deformation

95 Dorset, England

98 Geothermal Gradient: Near the Earth s surface the temperature increases with depth at a rate of about 25 degrees C per km.

99 Deformation type Causes Results Elastic temporary deformation Stress not greater than elastic limit of rock Strain released and shape returns to normal Brittle permanent break Plastic permanent ductile deformation Stress greater than yield point of rock (usually colder temperatures nearer surface rapid stress application) Stress greater than elastic limit of rock (usually higher temperatures deeper underground stress applied slowly over long time) Strain released with break in rock (faulting) Strain is permanent (folding)

100 Rocks buried at depth have stress being applied to it equally from all directions.

101 Plate Tectonics often applies stress to rocks that is not equal in every direction.

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105 Stress Type: Tension (results in thinning of the crust from being stretched).

106 Stress Type: Compression (results in thickening/shortening of the crust).

107 Stress Type: Shear (no change in crust thickness).

108 Stress types Plate boundaries Fault types Crustal thickening or thinning or both/none? Mountain types (if any) Compression Convergent Reverse (+ thrust) Thickening Fold and Thrust Tension Divergent Normal Thinning Fault-Block Shear Transform Strike-slip None None

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113 Fault Types Blind Thrust Fault Normal Fault Reverse Fault Strike-Slip Fault (Left-Lateral) Oblique-Slip Fault A Thrust Fault is a reverse fault with dip<45 degrees. A very low angle thrust fault is called an over-thrust.

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115 SHEAR SHEAR Left-Lateral STRIKE-SLIP Right-Lateral STRIKE-SLIP

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117 REVERSE NORMAL HW FW FW HW Compression Tension REVERSE NORMAL HW FW FW HW Tension Compression

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119 Glacier National Park What do you see?

120 Discuss with your neighbor the principle of superposition. Where is the oldest rock found?

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137 Y O O Y O Syncline North-Plunging Anticline South-Plunging Syncline Y

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141 What type of structure is this?

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143 Wallace Creek 143

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150 Additional Resources

151 Quantitative Reasoning #2: Question: If the middle of the Atlantic Ocean is discovered, by satellite imagery, to spread, on average, 2 inches per year, and assuming that rate has been fairly constant through the development of the Atlantic Ocean, when did spreading first begin? What do we know? 2 inches of spreading every 1 year OR 2 inches year Distance between the continental shelves of Africa and South America are ~5,000 km apart (5,000 km = 5 x 10 3 km) 1 inch = 2.54 cm 100 cm = 10 2 cm = 1 m 1000 m = 10 3 m = 1 km Math: 5 x 10 3 km x 10 3 m x 10 2 cm x 1 in = 5 x 10 3 x 10 3 x 10 2 in = 2 x 10 8 in 1 1 km 1 m 2.5 cm x 10 8 inchesx 1 year= 10 8 years or 10 2 x 10 6 years = 100 million years 1 2 in

152 Quantitative Reasoning #2: Question: If the fastest spreading center, which is the East Pacific Rise, spreads at a rate of 18 centimeters per year, and it s been spreading for 100 million years, how much new Pacific Ocean crust has been formed as a result? What do we know? 18 cm of spreading every 1 year OR 18 cm year 100 million years = 10 2 x 10 6 years = 10 8 years 100 cm = 10 2 cm = 1 m 1000 m = 10 3 m = 1 km Math: 10 8 years x 18 cm x 1 m x 1 km = 18 x 10 8 km= 18 x 10 8 km = 18 x 10 3 km 1 yr 10 2 cm 10 3 m 10 2 x = 18,000 km Earth s radius = 6400 km Circumference = 2πr = 40,192 km The Pacific Ocean should be ~ ½ the circumference of the planet? Is it? If not, where did it go?

153 Deformation type Causes Results

154 Additional Resources

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157 Measuring Speed and Direction Distance between hotspot and 9 m.y. rock is ~270 km. Speed = distance time Speed = 270km 9my

158 Measuring Speed and Direction 270km Speed = = 30 9my km my km my 10= cm yr

159 Measuring Speed and Direction km 30 10= my 3.0 cm yr

160 How fast is the Pacific Plate moving?

161 Solve then discuss with your neighbor make sure you both understand how to solve this type of problem. If a region with a rich gold deposit is cut by a fault that is known from other evidence to move at a rate of 4 cm/yr. The gold was deposited 10 million years ago. At what distance along the fault (in the direction of the fault movement) would one look for the other part of the gold deposit?

162 DEFINITIONS As ultramafic magmas rise through the crust, they leave high-density minerals behind, becoming less dense and hence also more basaltic and if travelling long enough or far enough, more felsic! Least dense FELSIC granitic -- continental crust Intermediate MAFIC basaltic -- oceanic crust + hotspots Most dense ULTRAMAFIC -- mantle rock

ANNOUNCEMENTS. Neighbor MEET & GREET. Turn to Neighbor: What is the difference between accretionary wedges and terranes?

ANNOUNCEMENTS. Neighbor MEET & GREET. Turn to Neighbor: What is the difference between accretionary wedges and terranes? ANNOUNCEMENTS THIS WEEK Thursday class: Please bring scissors! NEXT WEEK Wed CLASS: Bring a mechanical compass if have one. Neighbor MEET & GREET 1. Each person take out a sheet of paper and write LEGIBLY