HR: 16:00h
AN: GP34A-03    [Abstracts]
TI: New Contributions to the Geomagnetic Instability Time Scale: Paleomagnetic study of Tequila and Ceboruco-San Pedro-Amado Nervo Volcanic Fields (Trans Mexican Volcanic Belt)
AU: * Rodriguez Ceja, M
EM: maria@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria s/n, Mexico, 04510 Mexico
AU: Gogichaishvili, A
EM: avto@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: Rosas Elguera, J
EM: jrosas@ccip.udg.mx
AF: Centro de Ciencias de la Tierra, Universidad de Guadalajara, Ciudad Universitaria s/n, Guadalajara, 44840 Mexico
AU: Calvo, M
EM: mcalvo@ubu.es
AF: Dpto. de Fˇsica, E. P. S., Universidad de Burgos, Av. Cantabria, s/n, Burgos, Spain,
AU: Urrutia-Fucugauchi, J
EM: juf@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria s/n, Mexico, 04510 Mexico
AB: The Trans-Mexican Volcanic Belt (TMVB) is one of the largest continental volcanic arcs of the North American plate. It spans about 1000 km from the Pacific to the Gulf of Mexico. Despite the abundance of thick lava sequences with quite high extrusion rates, the TMVB have been relatively little studied from a paleomagnetic point of view. Previous studies were aimed for tectonic evolution of the region rather than documenting fluctuations of Earth's magnetic field in terms of both directions and intensity. We report a detailed paleomagnetic and rock-magnetic study of Tequila and Ceboruco-San Pedro-Amado Nervo volcanic fields. 350 oriented samples belonging to 31 independent cooling units were collected. All these sites were previously dated by means of the state-of-the-art 40Ar-39Ar geochronological method and span from 1.1 Ma to 2 Ky. Rock-magnetic experiments which included continuous susceptibility, isothermal remanence acquisition and hysteresis measurements point to simple magnetic mineralogy. In most of cases, the remanence is carried by Ti-poor titanomagnetite of pseudo-single-domain magnetic structure. The paleodirections of the flow dated as 819±25 ka correspond to a VGP latitude of 18° N. This anomalous field behaviour apparently recorded prior to the Matuyama-Brunhes reversal may coincide with the geomagnetic event, defined as M-B precursor. Two independent lava flows, dated as 623±91 and 614±16 ka respectively, yield reverse paleodirections and one lava flow dated as 690±29 yields transitional paleodirections. It is possible that these lavas erupted during the worldwide observable Big Lost or Delta events.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1522 Paleomagnetic secular variation
DE: 1530 Rapid time variations
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2005 Joint Assembly