Paleomagnetism of Miocene volcanics on Sao Tome: Paleosecular variation at the Equator and a comparison to its latitudinal dependence over the last 5 Myr

摘要: A collection was made in January 2009 of 10 oriented samples from each 54 sites lavas on Sao Tome Island (nominal location 0.3o N, 6.5o E). Some were affected by lightning leaving a total 42 for analysis paleosecular variation. Overall magnetic properties excellent (highly stable magnetizations carried pseudo-single domain magnetite). After principal component progressive alternating field demagnetization data the samples, twenty-two had normal polarity (D = 0. 6o, I -8.3o, α95 4.3o, κ 53.1) and 20 reverse 176.0o, 4.2o, 7.3o, 20.8); directions are within 5° antiparallel, yielding positive reversal test. The combined set site mean virtual geomagnetic poles converted to common (normal) yields pole position at 86.0°N, 211.5oE, A95=3.1o. Ar/Ar K/Ar dating reveals that these rocks Miocene age (∼5–11 Ma), old enough allow northerly plate motion help explain slightly far-sided position. between-site dispersion estimated as angular standard deviation, Sb, equaled 11.4° with 95% confidence interval between 9.9° 13.4°. This article is protected copyright. All rights reserved.