Paleomagnetic and rock-magnetic study of Los Azufres lava flows (central Mexico)

Abstract

We report a detailed rock-magnetic and paleomagnetic investigation on seventeen volcanic units (160 standard paleomagnetic cores) belonging to essentially Plio-Pleistocene Azufres Volcanic Field, located in the central part of the Trans-Mexican Volcanic Belt. Titanium-poor titanomagnetite is responsible for thermoremanence in the most lava flows, while unstable titanomaghemites presumably dominate in the less than half of the analyzed lava flows. The mean paleodirections are calculated for 15 sites, discarding apparently transitional flow and poorly defined (scattered) units yielding Dec = 357.23°, Inc = 38.62°, α95 = 4.89°, k = 55. These values are concordant with the expected paleodirections derived from the stable North America reference paleomagnetic poles. Secular variation parameters calculated through the dispersion of the site-mean virtual geomagnetic poles and the inclination anomaly are found slightly different to the available models. Within the 17 paleodirections obtained, four lava flows are normally magnetized between 1.14 and 1.23 Ma. These paleodirections may tentatively be assigned to the worldwide observable Cobb Mountain Geomagnetic event (subchron). This presumably short-lived episode seems to be characterized by apparently major duration than previously reported.