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Geomagnetic Polarity Epochs: Sierra Nevada II
Science (New York, N.Y.)
|October 18, 1963
Summary
New studies on Sierra Nevada volcanic rocks reveal two distinct magnetic groups, suggesting Earth's magnetic field reversals, not mineralogy, dictate polarity. These findings align with radiometric dating, detailing the length of past magnetic epochs.
Area of Science:
- Geophysics
- Paleomagnetism
- Volcanology
Background:
- Understanding Earth's magnetic field reversals is crucial for paleomagnetic studies.
- Volcanic rocks record the Earth's magnetic field at the time of their formation.
Purpose of the Study:
- To investigate the magnetic properties of recent volcanic extrusions in the Sierra Nevada.
- To determine the cause of opposing magnetic polarities observed in these volcanic rocks.
Main Methods:
- Potassium-argon dating to determine the age of volcanic extrusions.
- Analysis of remanent magnetization in volcanic samples.
- Thermomagnetic experiments and mineralogic studies.
Main Results:
- Identified two groups of remanent magnetization: normal (downward, north) and reversed (upward, south).
- Mineralogic studies did not explain the opposing polarities, supporting a geomagnetic origin.
- Radiometric ages are consistent with Earth's magnetic field reversals.
Conclusions:
- The observed magnetic polarities in Sierra Nevada volcanic rocks reflect reversals of Earth's main dipole field.
- The durations of recent polarity epochs (N1, R1, N2) were estimated based on radiometric ages.
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