Abstract

The transitional behavior exhibited by Earth's magnetic field during polarity reversals holds the key to understanding the complexities of the field. Interpretation of the severely limited reversal data set, however, remains controversial. Discussion centers around the nature of pole paths during transitions and their possible relation to other geophysical phenomena. Paleomagnetic data from Volcan Tatara-San Pedro in the central Chilean Andes (lat 36°S, long 71°W) provide the first record of the Matuyama-Brunhes reversal from South America and only the third transitional record from the Southern Hemisphere. A stratigraphic section of ten lava flows yielded intermediate pole positions that center in Australia; the mean pole is 16.8°S, 133.0°E. K-Ar analyses of two of these flows provided dates of 768 ±8 ka and 763 ±14 ka, ages coincident with the established Matuyama-Brunhes boundary. The clustering of these transitional poles strengthens the hypothesis that Earth's magnetic field retains a strong dipole component during reversals.

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