HR: 16:35h
AN: GP24A-02 INVITED     [Abstracts]
TI: Tectonics Along Western-Central Part of the Trans Mexican Volcanic Belt as Inferred From Palaeomagnetic Data: A Summary
AU: * Rosas-Elguera, J
EM: jrosaselguera@yahoo.com
AF: Centro Universitario de Ciencias Exactas e Ingenierias, Universidad de Guadalajara, Av. Revolucion No. 1500, Modilo "O" planta alta, Guadalajara, Jal 44840,
AU: Goguichaisvilli, A
EM: avto@geofisica.unam.mx
AF: Laboratorio de Paleomagnetismo, UNAM, Circuito Interior, Delegacion Coyoacan, Mexico, 04510, Mexico
AU: Alva-Valdivia, L
EM: lalva@geofisica.unam.mx
AF: Laboratorio de Paleomagnetismo, UNAM, Circuito Interior, Delegacion Coyoacan, Mexico, 04510, Mexico
AU: Urrutia-Fucugauchi, J
EM: juf@geofisica.unam.mx
AF: Laboratorio de Paleomagnetismo, UNAM, Circuito Interior, Delegacion Coyoacan, Mexico, 04510, Mexico
AB: The Trans-Mexican Volcanic Belt (TMVB), one of the largest continental volcanic arcs built on the North America plate, spans about 1000 km and crosses central Mexico from the Pacific Ocean to the Gulf of Mexico. The initial stage of the TMVB is marked by widespread Miocene basaltic volcanism, emplaced from the Nayarit state, in the west, to the longitude of Mexico City. This volcanism is characterized by plateau-like structures resulting from the shield volcanoes and fissure lava flows, which have an estimated aggregate volume ranging between 3200 and 6800 km3. The western-central Mexico has been affected by right-lateral transtension within the western TMVB but previous paleomagnetic studies indicate some 15-20° anticlockwise tectonic rotations for the Rio Grande de Santiago canyon and surrounding areas, in accordance with a Miocene left-lateral transtensional tectonic regime. We present a summary of paleomagnetic and rock-magnetic studies of that Miocene volcanic succession from the TMVB. A total of 114 consecutive basaltic lava flows (more than 550 oriented samples) were collected from four localities: Tepic, Guadalajara, Los Altos, and Queretaro which span from 11 to 7.5 Ma. The mean paleodirection obtained for Tepic area is I = 33.7°, D = 358.4°, k = 140, á95 = 3.0°, N = 17. These directions are in perfect agreement with the expected paleodirections for late Miocene time, as derived from reference poles given by Besse and Courtillot (1991) for North America.. The mean paleodirection obtained for Guadalajara is I = 31.1°, D = 354.6°, k = 124, 95 = 2.1°, which corresponds to the mean paleomagnetic pole position Plat = 84°, Plong = 129.8°, k = 29, 95 = 4.4°. These directions are in reasonably good agreement with the expected paleodirections for middle Miocene time. The mean paleomagnetic direction calculated for Los Altos and Queretaro is I = 32.46°, D = 341.2°, k = 7.2 and 95 = 11.6°. Thus, our results suggest that no major block rotation has occurred in the Nayarit and Guadalajara areas since about 10 Ma but 20° anticlockwise tectonic rotations for the Los Altos and Queretro areas is in accordance with the proposed left-lateral transtensional tectonic regime.
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 1527 Paleomagnetism applied to geologic processes
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly