Paleomagnetism of Ar-Ar dated lava flows from the Ceboruco-San Pedro volcanic field (western Mexico): Evidence for the Matuyama-Brunhes transition precursor and a fully reversed geomagnetic event in the Brunhes chron

Marie Petronille (1) , Avto Goguitchaichvili , Bernard Henry (2) , Luis M. Alva-Valdivia , José Rosas-Elguera , Jaime Urrutia-Fucugauchi , Maria Rodriguez Cejá , Manuel Calvo-Rathert

1 ENS-PSL - École normale supérieure - Paris
2 IPGP - Institut de Physique du Globe de Paris

We report a detailed paleomagnetic and rock magnetic study of 17 independent lava flows belonging to the Trans-Mexican Volcanic Belt; 175 oriented samples were collected in the Ceboruco-San Pedro volcanic field. These sites were previously dated by means of a state-of-the-art ⁴⁰Ar-³⁹Ar geochronological method and span from 819 to 2 ka. Rock magnetic experiments, which included continuous susceptibility and hysteresis measurements, point to simple magnetic mineralogy. In most cases, the remanence is carried by Ti-poor titanomagnetite of pseudosingle-domain magnetic structure. Fourteen flows give normal magnetic polarities, while two are reversely magnetized; only one cooling unit yields intermediate paleodirections. The paleodirections of the flow dated at 819 ± 25 ka correspond to a VGP latitude of 18°N. This anomalous field behavior apparently recorded prior to the Matuyama-Brunhes (M-B) reversal may coincide with the transitionally magnetized lavas on La Palma, Canary Islands (⁴⁰Ar-³⁹Ar age of 822.2 ± 8.7 ka), and with an event featured in several marine sediment records. Thus this geomagnetic event, defined as M-B precursor, is probably global in extent. Two independent lava flows, dated at 623 ± 91 and 614 ± 16 ka, yield reverse paleodirections. Age uncertainties make it difficult to claim the discovery of a new geomagnetic event. It is possible that these lavas erupted during the worldwide observable Big Lost event (⁴⁰Ar-³⁹Ar age of 580.2 ± 7.8 ka), which has probably been longer and more complex than it is generally believed for geomagnetic excursions.

Domaines: Planète et Univers [physics]

Marie Petronille, Avto Goguitchaichvili, Bernard Henry, Luis M. Alva-Valdivia, José Rosas-Elguera, et al.. Paleomagnetism of Ar-Ar dated lava flows from the Ceboruco-San Pedro volcanic field (western Mexico): Evidence for the Matuyama-Brunhes transition precursor and a fully reversed geomagnetic event in the Brunhes chron. Journal of Geophysical Research : Solid Earth, 2005, 110, pp. 655-675. ⟨10.1029/2004JB003321⟩. ⟨insu-03601112⟩