Paleomagnetic study of lavas from the Popocatepetl volcanic region, central Mexico
Por:
Conte G., Urrutia-Fucugauchi J., Goguitchaichvili A., Soler-Arechalde A.M., Morton-Bermea O., Incoronato A.
Publicada:
1 ene 2004
Resumen:
Results are presented for a paleodirectional and paleointensity study of 16 Popocatepetl lava flows. Popocatepetl is a tall, active, dacitic-andesitic stratovolcano: it forms the southern end of a N-S-trending Quaternary volcanic range at the eastern edge of the Basin of Mexico. Studied units are mainly andesites and one trachyandestite, and all possess similar trace- and rare-earth-element compositions. Rock-magnetic experiments show that remanence is carried in most cases by Ti-poor titanomagnetite, resulting from oxy-exsolution of original titanomagnetite during flow cooling. Unblocking temperature spectra and high coercivities point to "small" pseudo-single domain magnetic grains for these (titano)magnetites. Single-component, linear demagnetization plots were observed in most cases. A strong, lightning-produced magnetization overprint was detected for one site. Combining the new paleomagnetic data provides a mean paleodirection of I = 35.4°, D = 345.7°, k = 21, ?95 = 8.5°, N = 15 for the Popocatepetl volcano region. All studied flow yield normal polarity magnetization, which supports a maximum age within the Brunhes chron. Twenty-five samples were selected for Thellier palaeointensity experiments based on magnetic properties, stable single-component remanent magnetizations, and reasonably reversible continuous thermomagnetic curves. Fourteen samples from four different flows yield reliable paleointensity estimates with the flow-mean virtual dipole moments (VDM) ranging from 5.9 to 9.2 × 1022 Am2. The NRM fractions used for paleointensity determination range from 35 to 96%, and the quality factors vary between 3.4 and 46.9, being normally greater than 6. Mean VDM obtained in this study is 7.2 ± 1.4 × 1022 Am2, slightly lower than the present-day dipolar value. © 2004 by V. H. Winston and Son, Inc. All rights reserved.
Filiaciones:
Laboratorio de Paleomagnetismo y Geofisica Nuclear, Instituto de Geofisica, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, México D.F., 04510, Mexico
University of Naples Federico II, Earth Science Department, Naples, Italy
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