HR: 16:15h
AN: GP34A-04    [Abstracts]
TI: Long-Term Variation of Geomagnetic Field Strength - Contributions from Latinamerica
AU: * Gogichaishvili, A
EM: avto@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria s/n, Mexico, 04510 Mexico
AU: Morales, J
EM: jmorales@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria s/n, Mexico, 04510 Mexico
AU: Alva-Valdivia, L
EM: lalva@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria s/n, Mexico, 04510 Mexico
AU: Urrutia-Fucugauchi, J
EM: juf@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria s/n, Mexico, 04510 Mexico
AB: Study of the long-term variation of polarity and paleodirection of the Earth's magnetic field in the Precambrian and Phanerozoic has proved valuable in geosciences. Magnetic polarity in the Mesozoic and Cenozoic is fairly well-established, with some first- order trends defined for older times. Defining of comparable long-term Earth's dipole moment variation has proved far more difficult an understanding. Among many other findings, magnetic polarity studies have defined several first-order features like the Permo-Triassic and Cretaceous superchrons, characterized by constant reverse and normal polarity, respectively, over long intervals. The proposal of even longer dipole moment characteristic features in the geologic past, like a low dipole moment during most of the Mesozoic, has important implications for the geodynamo. Since 1999, we are engaged to determine the Earth's field intensity during Miocene, late Paleozoic and Mesozoic using dated basalt units mainly from Mexico (Trans-Mexican Volcanic Belt and Baja California Peninsula) and South America (Brazil, Chile and Argentina). We will discuss three major issues currently debated: (1) paleointensities during a large period of Mesozoic (260-120 My) to examine the question of unusually low field known as "Mesozoic Dipole Low". (2) mid-Cretaceous paleointensities to examine theoretically predicted abnormally high intensity during the CNS and (3) paleointensities from 5 to 60 My old volcanic rocks.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1510 Dynamo theories
DE: 1521 Paleointensity
DE: 1522 Paleomagnetic secular variation
DE: 1560 Time variations--secular and long term
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2005 Joint Assembly