Paleomagnetic and rock-magnetic survey of Brunhes lava flows from Tancitaro volcano, Mexico

Abstract

This study presents paleomagnetic results from Tancitaro volcanism in the Michoacan Guanajuato Volcanic Field, western Mexico, as a contribution to the time averaged field global database. Detailed paleomagnetic and rock–magnetic studies were carried out on eleven independent lava flows; 120 oriented, standard paleomagnetic cores were collected from Tancitaro volcano and surrounding areas. All sites were dated by means of ⁴⁰Ar–³⁹Ar (Ownby et al., 2007) as originating from 793 ka to present. Rock–magnetic experiments included continuous susceptibility and hysteresis measurements. Remanence is carried mostly by Ti–poor titanomagnetite of pseudo–single–domain magnetic structure. Eight out of eleven flows yield normal magnetic polarities while three sites yielded inconsistent paleodirections most probably due to lightning. Mean paleodirection from eight flows is Inc=39.5°, Dec=356.4°, k=29, αc₉₅=9.1° which corresponds to a pole position with Plat=84.4°, Plong=219.9°, K=33 and A₉₅=8.5°, practically undistinguishable from expected Plio–Quaternary paleodirections, for the North American Craton. Paleosecular variation is compatible with other studies at the same latitude bands and with recent statistical models. The mean inclination falls within the uncertainties of the Geomagnetic Axial Dipole plus 5% quadrupolar contributions.