MATUYAMA-BRUNHES TRANSITION RECORDED IN LAVA FLOWS OF THE CHILEAN ANDES - EVIDENCE FOR DIPOLAR FIELDS DURING REVERSALS

The transitional behavior exhibited by Earth's magnetic field during p olarity reversals holds the key to understanding the complexities of t he field. Interpretation of the severely limited reversal data set, ho wever, remains controversial. Discussion centers around the nature of pole paths during transitions and their possible relation to other geo physical phenomena. Paleomagnetic data from Volcan Tatara-San Pedro in the central Chilean Andes (lat 36-degrees-S, long 71-degrees-W) provi de the first record of the Matuyama-Brunhes reversal from South Americ a and only the third transitional record from the Southern Hemisphere. A stratigraphic section of ten lava flows yielded intermediate pole p ositions that center in Australia; the mean pole is 16.8-degrees-S, 13 3.0-degrees-E. K-Ar analyses of two of these flows provided dates of 7 68 +/- 8 ka and 763 +/- 14 ka, ages coincident with the established Ma tuyama-Brunhes boundary. The clustering of these transitional poles st rengthens the hypothesis that Earth's magnetic field retains a strong dipole component during reversals.