Geo Review3 - 1 What does it mean that the earth has an AGD...

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1. What does it mean that the earth has an AGD magnetic field? What does it mean that the field “reverses”? Axial Geocentric Dipole – The average of magnetic position is exactly center. This means that the magnetism of the earth over time, on average, is at the center of the earth. Geomagnetic reversal is the process in which the magnetic north and south poles, well, reverse. This is thought to be a result of dynamo theory. 2. What is secular variation? Does the pole wander? The changes in location and intensity of the earth’s magnetic field are called secular variation. Yes the pole wanders. 3. What is a magnetic anomaly? How do they arise? Why do anomalies over the ocean floor occur as bands? Are there stripes on the ocean floor? Magnetic anomaly is the difference between the expected magnetic strength of a location and the measured magnetic strength. These arise on the ocean floor as bands as a result of sea floor spreading. The magnetic minerals in basalts are aligned with the magnetic field at the time of crystallization, and over time, recording the changes in the earth’s magnetic fields (paleomagnetism). 4. How does a rock become permanently magnetized? What is the “curie temperature”? A rock can become permanently magnetized in the presence of an external magnetic field during crystallization. When magmas cool the magnetic minerals (magnetite) become permanently magnetized parallel to the earth’s magnetic field. The curie temperature is the point at which magnetic a ferromagnetic material loses its permanent magnetism. Above the curie point those materials may be acted upon by an external magnetic field. 5. What kind of structures are produced at a rifting continent? What rock sequences are produced during the rift phase of continental divergence? During the drift phase? Continental rifting: o Brittle fracture in the crust, and ductile necking in the mantle. Faulting occurs along the crust as the crust thins and falls into a basin, creating a rift valley. o
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This note was uploaded on 04/09/2008 for the course GEOL 11 taught by Professor Tekla during the Fall '06 term at UMass (Amherst).

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Geo Review3 - 1 What does it mean that the earth has an AGD...

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