Palaeosecular Variation Recorded by 9 ka to 2.5-Ma-old Lavas from Martinique Island: New Evidence for the La Palma Aborted Reversal ∼617 ka Ago

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Geomagnetic excursions, Magnetic field, Magnetic mineralogy and petrology, Magnetostratigraphy, Palaeomagnetic secular variation, Reversals: process, time scale, magnetostratigraphy

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Fifteen sites of lava flows from Martinique Island (FWI) have been selected to document the geomagnetic field in the Caribbean area over the past 2.5 Ma and further constrain the time-averaged field during this period. Identical characteristic directions were isolated using both AF and thermal stepwise demagnetization techniques in all flows. Nine mean-site directions have a normal polarity, while three others are reversed. The mean geomagnetic pole position obtained after reducing all directions to the same polarity is indistinguishable from the present north geographic pole. The dispersion is at least 8° larger than the values derived from the time-averaged field models and remains unexplained otherwise than resulting from the relatively small number of directions. The other three flows are characterized by large deviations from the expected north–south direction. One lava flow dated at 1.69 Ma (±0.02 Ma) is likely associated with a transitional field during the Gilsà subchron. The lava flow dated at 770 ka (±11 ka) coincides with the age of the Brunhes-Matuyama geomagnetic reversal and is also coeval with another intermediate flow of the same age found at Guadeloupe Island. The 617 ka (±52 ka) old unit is characterized by reversed directions that are evidently not related to the last reversal, but with other reversed polarity and transitional lava flows of the same age recorded, respectively at Mexico and La Palma island. We infer that the presence of reversed directions with the same age at distinct localities confirms that a short episode of reversed polarity has occurred during this period.

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Geophysical Journal International, v. 200, issue 2, p. 917-934