Paleomagnetism and age constraints of historical lava flows from the El Jorullo volcano, Michoacán, Mexico

Abstract

The present study employs petrology, rock magnetics, and paleointensity on four lava flows (seven sites) of the El Jorullo volcano; a historical (1759–1766 AD) cinder cone in the Michoacán-Guanajuato Volcanic Field. El Jorullo lava flows cover an extensive area of ∼10.8 Km2, and a volume ∼0.35 Km3. Rock-magnetic experiments and microscopic observations reveal pseudo-single domain size Ti-poor titanomagnetite as the main carrier of magnetization in all sampled flows. Notably the calculated mean direction from all the sites show a slight westwards bias when compared against the secular variation global models. The mean paleo-direction for the El Jorullo historical eruption is: Dec = 2.5°, Inc = 37.5°, kappa = 214, α95 = 1.8, N = 31; the Virtual Geomagnetic Pole has Plat = 87° N, Plong = 307° E, Kappa = 260, A95 = 1.6; paleointensity data: 45.4 ± 3.6 μT; and Virtual Dipole Moment: 10.3 ± 1 × 1022 Am2. The paleodirections and the paleointensity values from these lava flows are well-constrained and reliable. These results allow to improve the accuracy and reliability of the global and regional secular variation models available for the last centuries.