Comment on all the reasons why the magnetic profiles in the figure are not exact
ID: 292966 • Letter: C
Question
Comment on all the reasons why the magnetic profiles in the figure are not exactly symmetric across the ridge?
Age (Ma) 80 70 60 50 40 30 20 10 model SOUTH ATLANTIC Distance (km) 1000 1500 500 data model NORTH PACIFIC 1000 Distance (km) 500 SOUTH PACIFIC o Distance (km) 500 1000 1800 1500 Figure 3.12. The geomagnetic-reversal timescale for the last 80 Ma as proposedin 1968. The magnetic-anomaly profiles with their model profiles and model reversal sequences are shown for the South Atlantic, North Pacific and South Pacific. The South Atlantic timescale was made by assuming that the spreading rate there has been constant for the last 80 Ma. In comparison, spreading in the Pacific has clearly been both faster and more irregular (note the different distance scales for the Pacific lines connect specific magnetic anomalies numbered as in Fig. 3.14 After Heirtzler et al. (1968).)Explanation / Answer
Magnetic profiles are formed in the divergent boundary where two plates are spreading away from each other forming a fissure in between them and magma rises through this fissure to form oceanic ridges. Geophysical evidence showed that the magnetic profile formed on the either side of ridge axis from the basaltic layer of oceanic crust as basalt rocks generate temperature remnant magnetism (TRM).
The magnetic profile on either side of the oceanic ridge is not symmetrical due to magnetic reversal. From the palaeo proterozoic rock records, it has been found that the some rocks show normal magnetic direction and some show reversed magnetic direction to the Earth's magnetic direction. Normal magnetic anomaly is associated with positive anomaly and reversed is associated with negative anomaly. The magnetometer showed that the positive and negative anomalies are symmetrical on either side of ridge due to periodic reversal took place thrughout the geologic time.
If the magnetic profile is not symmetrical it indicates there were no periodic magnetism and reversal of magnetism.