study guide exam 2 - Exam 2 Study Guide I Seafloor...

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Exam 2 Study Guide I. Seafloor Spreading: Hess’s and Dietz’s theory a. What is the theory?: The gradual spreading of an ocean basin as new oceanic curst forms at a mid-ocean ridge axis and then moves away from the axis. Hot magma rises from the mantle to create new oceanic crust, which then moves away from the top of the ridge in conveyor-belt fashion. b. Evidence & Proof for it: Vine & Mathew’s Ideas - The Earth has magnetic poles at the north and south poles. Throughout history the polarity of the Earth’s poles have changed from normal polarity to reverse polarity. During times of normal polarity, any rocks that were formed had normal polarity as well, and vice versa. - Since the seafloor is constantly spreading and forming new crust, which also keeps its polarity, the polarity of the newly formed crust will keep that polarity, even if the polarity of the Earth should reverse. - Therefore, the crust formed as a result of seafloor spreading has symmetrical stripes of reverse and normal polarity crust. (This is seafloor magnetic anomalies.) c. The deeper and further away the oceanic lithosphere is from the mid-ocean ridge, the older that part of the crust is. II. Subduction Zones a. When an oceanic plate runs into another oceanic plate or a continental plate, subduction occurs. Subduction occurs when these two plates collide, and since they have no other place to move, one begins to sink beneath the other. Areas where this occurs are called subduction zones. b. Subduction zones are also known as trenches. c. With the formation of subduction zones also comes the formation of accretionary prisms. Accretionary prisms form the same way a pile of snow in front of a plow does. When a plate submerges under another, sediment bunches up on the continent. Behind the accretionary prisms, volcanic arcs form. d.
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study guide exam 2 - Exam 2 Study Guide I Seafloor...

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