Where does the lithosphere of the Atlantic Ocean form?
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At the boundary between the Caribbean Plate and the South American plate |
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At the Cocos plate |
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At the mid-Atlantic Ridge |
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At the passive margin found on the east coast of the U.S. |
Does the plate on which the United States resides consist of continental lithosphere, oceanic lithosphere or both?
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continental only |
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oceanic only |
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both continental and oceanic lithosphere |
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Neither continental nor oceanic lithosphere |
When considering magnetic anomalies and how they are preserved at spreading centers, are individual anomalies oriented parallel or oblique (perpendicular) to ridge crests?
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oblique (perpendicular to) |
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parallel to |
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they are completely randomly oriented with respect to the ridge crest. |
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some are oriented parallel and some are oblique to the ridge crest |
Some magnetic stripes are wider than others. Why?
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The rate of spreading changed through time. |
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The duration of each anomaly is different. |
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All of the above are potential explanations for why the stripes could vary in width. |
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The variation in width of the anomalies do not tell us anything about the history of the Earth or the conditions that existed when rocks formed at the bottom of the ocean. |
What is the width of the South Pacific Ocean (as measured from the data of the East Pacific Rise)?
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4.2 km |
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80 km |
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6,000 km |
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3,000 km |
What is the average spreading rate of the East Pacific Rise (in km/million yrs)?
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7.5 x 10^-5 km/million yrs |
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75 km/million yrs |
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37.5 km/million yrs |
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1.8 x 10^-5 km/million yrs |
Based on arc-trench geometry and the fact that melting typically occurs at about the same depth in the subduction zones, what is the major factor that controls the width of the arc-trench gap?
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The angle, or steepness, of the subducting plate. |
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The composition of the mantle directly below the trench |
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The thickness of the continental crust under which the oceanic plate is subducting |
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The amount of water overlying the trench |
How does the point where melting occurs relate to the position of the volcanic arc?
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It is always closer to the trench than to the island arc |
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There is no defined relationship between the area where melting occurs and the placement of the volcanic arc. |
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It is situated approximately 200 miles, geographically, from where the volcanic arc forms |
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It is situated directly below the area where the volcanic arc forms |
What is the width of the Arc-Trench gap at the Skwentna segment of the subduction zone? (in kilometers)
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460 km |
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480 km |
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200 km |
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260 km |
What is the approximate angle of subduction of the Amchitka segment of the subduction zone?
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15 degrees |
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45 degrees |
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5 degrees |
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30 degrees |
