Adapted from Shea, J.H. (Nov 1988). Understanding Magnetic Anomalies and Their S

Question

Adapted from Shea, J.H. (Nov 1988). Understanding Magnetic Anomalies and Their Significance. Journal of Geological Education, 36(5),

Magnetic profile across the East Pacific Rise at 51.6? S (east side).

from Shea, J.H. (Nov 1988). Understanding Magnetic Anomalies and Their Significance. Journal of Geological Education, 36(5),

Magnetic profile across the East Pacific Rise at 51.6? S (west side).

Is there a reasonable degree of mirror-image symmetry in these patterns? In other words, do you think that the patterns show the same general shape on opposite sides of the ridge? Explain.

Explanation / Answer

Yes, there is a reasonable degree of mirror-image symmetry in the magnetic anomaly patterns on opposite sides of the ridge. This occurs due to the sea-floor spreading. Marine magnetic anomaly is the variation in the strength of Earth's magnetic field caused by magnetism in the rocks of the ocean floor. These rocks of the ocean floor are created when magma rises up through the ridge and solidifies. The sea floor spreads to either side of the ridge under the influence of many factors allowing new magma from the depths of the ridge to rise to the surface. At the time of cooling and solidification the magma acquires a magnetic orientation parallel to the magnetic field of the earth. But Earth's magnetic field changes polarity from time to time. As a result the polarity of the magnetic orientation of the magma solidified at different times also have opposite polarities. Since the sea floor spreading will be equal on both sides of the ridge, we can find same polarity anomalies at equal distances on either side of the ridge. That is why we have here a mirror image symmetry in the magnetic anomaly pattern on opposite sides of the ridge.

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