Open AccessTime‐averaged field at the equator: Results from Ecuador
Author(s) -
Opdyke Neil D.,
Hall Minard,
Mejia Victoria,
Huang Kainian,
Foster David A.
Publication year - 2006
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2005gc001221
Subject(s) - declination , geology , magnetic declination , paleomagnetism , equator , latitude , geodesy , field (mathematics) , magnetic dip , magnetostratigraphy , paleontology , seismology , geophysics , magnetic field , astrophysics , earth's magnetic field , physics , mathematics , quantum mechanics , pure mathematics
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 α 95 of 10° or less; 21 flows yielded normal directions of magnetization (declination = 354.6°, inclination = −5°, α 95 = 7.2°) and 30 yielded reverse (declination = 183.5°, inclination = 5.6°, α 95 = 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 α 95 = 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 × 10 22 to 22.6 × 10 22 Am 2 . The mean value for the reverse field is 3.2 × 10 22 Am 2 , while for the normal field it is 10.2 × 10 22 Am 2 . The 40 Ar/ 39 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.