HR: 0800h
AN: GP31C-02    [Abstracts]
TI: 10 Ma of Igneous Activity in the Transmexican Volcanic Belt: Tectonic and Geomagnetic Implications.
AU: * Ruiz-Martinez, V C
EM: vcarlos@fis.ucm.es
AF: Dpto Geofisica, Fac CC Fisicas, Universidad Complutense de Madrid, Avda Complutense s/n, Madrid, 28040, Spain
AU: Osete, M L
EM: mlosete@fis.ucm.es
AF: Dpto Geofisica, Fac CC Fisicas, Universidad Complutense de Madrid, Avda Complutense s/n, Madrid, 28040, Spain
AU: Urrutia-Fucugauchi, J
EM: juf@geofisica.unam.mx
AF: Instituto Geofisica, Universidad Autonoma de Mexico, Ciudad Universitaria, Del Coyoacan, Mexico D.F., 04510, Mexico
AB: A total of 51 sites with geochronological control were sampled in the central and western segments of the Transmexican Volcanic Belt (TMVB). Together with other previously published 69 sites from the eastern segment, they span the spatial and temporal activity of the TMVB. Using now the same reference directions and methodologies, they are analyzed in order (i) to determine the possible occurrence and significance (spatially and temporally) of vertical axis crustal block rotations that have been reported in this region; and (ii) to study the geomagnetic Paleo Secular Variation during the last 10 Ma; to check the previously suggested existence of a "Pacific Dipole Window" extending to Mexico. Paleomagnetic results, backed by statistical tests performed according to their geographical distribution (3 structural segments) or according to their ages (Late Miocene, Pliocene or Quaternary), do not support the notion that large vertical axis block rotations (paleomagnetically detectable) occurred in this arc after Late Miocene times. They suggest that the TMVB could be considered paleomagnetically as an unique tectonic domain under a transtensional regime, where its extension component prevails over its left-lateral component. The mean paleomagnetic directions, obtained in the age ranges 10-5 Ma and 5-0 Ma, do not differ from their respective reference directions. In both datasets, VGPs have been selected using quality Fisher's precision parameters and optimum cutoff angles. This results in a circularly symmetrical data distribution with statistically indistinguishable antipodal normal and reverse polarities. VGP dispersions are consistent with those from globally distributed observations at Mexican latitudes for the Miocene and the Plio- Quaternary. An analysis of all the published paleomagnetic data from the TMVB, when combined all together and selected in the same terms, do not support neither the existence of large crustal block rotations nor the persistence of a magnetic anomaly in the studied region.
UR: http:www.minas.upm.es/fundacion/jgs/ftproot/2003- 2004/GrupoA/VCRuiz/VCRuiz.pdf DE: 1513 Geomagnetic excursions
DE: 1522 Paleomagnetic secular variation
DE: 1525 Paleomagnetism applied to tectonics: regional, global
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly