HR: 0800h
AN: GP11D-0864    [Abstracts]
TI: Paleomagnetic and magnetic fabric studies of the San Gaspar ignimbrite, western Mexico - constraints on emplacement mode and source vents
AU: * Rosas-Elguera, J
EM: jrosas@ccip.udg.mx
AF: Universidad de Guadalajara, Av. Revolución No. 1500, Guadalajara, Jal 44840 Mexico
AU: Alva-Valdivia, L
EM: lalva@tonatiuh.igeofcu.unam.mx
AF: Lab. Paleomagnetismo, Ciudad Universitaria, D.F., Mex 04510 Mexico
AU: Goguitchaisvili, A
EM: avto@tonatiuh.igeofcu.unam.mx
AF: Lab. Paleomagnetismo, Ciudad Universitaria, D.F., Mex 04510 Mexico
AB: Paleomagnetic and magnetic fabric data for the 4.8 Ma San Gaspar ignimbrite, one of the largest in western Mexico, are used to investigate on the source vents and emplacement mechanism. Rock-magnetic properties are similar, suggesting relatively homogeneous mineralogy of the unit. Isothermal remanence and continuous susceptibility-temperature experiments point to low to medium-Ti titanomagnetite as the main ferromagnetic mineral. Hysteresis parameters of most samples fall in the pseudo-single-domain grain size region; wasp-waisted hysteresis loops were identified corresponding to high Hcr/Hc values. Stepwise thermal and alternating field demagnetization shows that secondary components are negligible, and always completely removed below 20 mT or 400øC. Thereafter, the characteristic component is isolated with small within-site dispersion of mean direction ( 95<10ø at 7 out of 10 sites). The within-site consistency of directional features of magnetic fabric supports that the ignimbrite welded and cooled in situ and was probably emplaced in NW-SE rift zone from a single eruption center located south or east of a younger Pleistocene caldera. Paleomagnetic, rock-magnetic and ore microscopy data support the hypothesis that the extensive and widespread ignimbrite deposits in western Mexico correspond to a major explosive volcanic phase in the Pliocene.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting