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Time-averaged field at the equator: Results from Ecuador

Abstract:

Seventy sites were collected from Pliocene to recent lavas in Ecuador between 0.19° and 1.1°S latitude. Lightning affected many of the sites sampled, and the final data set consisted of 51 sites with α95 of 10° or less; 21 flows yielded normal directions of magnetization (declination = 354.6°, inclination = -5° α95 = 7.2°) and 30 yielded reverse (declination = 183.5°, inclination = 5.6°, a95 = 5°). These sites pass a reversal test at a high level. The combined data give a direction of declination = 359.9°, inclination = -5.4°, and a95 = 4.2°, which is just significantly different from the GAD field but is in agreement with a GAD field plus 5% quadrupole field. Mean VGPs are not significantly different from the geographic poles. The ASD for the combined sites is 13.3°, which is in agreement with model "G. " Paleointensity measurements yield values of VADM, which range from 1.39 × 1022 to 22.6 × 1022 Am2. The mean value for the reverse field is 3.2 × 1022 Am2, while for the normal field it is 10.2 × 1022 Am2. The <sup>40</sup>Ar/<sup>39</sup>Ar dates on selected sites show that they are 2.6 Ma and younger. The age dates and magnetic polarity indicate that the Chacana structure is Brunhes/Matuyama in age. Copyright 2006 by the American Geophysical Union.