Comprehensive paleomagnetic study of a succession of Holocene olivine-basalt flow: Xitle Volcano (Mexico) revisited

Abstract

Abstract A detailed paleomagnetic study of a young Late Holocene olivine-basalt flow from the Xitle volcano in the southern Basin of Mexico was completed to evaluate the consistency and reliability of the record derived from fresh well-preserved and exposed lava flows. One-hundred oriented standard paleomagnetic cores corresponding to 10 different lava effusion episodes were collected from unit-flow V. Thermomagnetic analyses show that bulk magnetic properties and remanence is carried in most cases by Ti-poor titanomagnetite, presumably resulting from oxy-exsolution processes during the initial flow cooling. Unblocking temperature and coercivity suggests pseudo-single domain magnetic grains for these (titano)magnetites. Thermal and alternating field demagnetizations show well-defined univectorial magnetizations. Most sites present a mean direction with small angular dispersion around the dipolar direction for central Mexico. The overall mean direction (N = 10, Dec = 1.1°, Inc = 34.1°, k = 531 and α95 = 2.1°) is characterized by small angular dispersion and inclination close to the dipolar value for the locality. Anisotropy ofmagnetic susceptibility lineation agrees with the geologically-inferred flow direction. Various samples from the 10 lava flows were selected for Thellier paleointensity experiments because of their stable remanent magnetization and relatively low within-site dispersion. According to reliability parameters, the obtained paleointensities are of reasonably good quality. Nine mean paleointensities range between 48.6 and 73.9 μT. The overall mean paleointensity of 59.9–7.7 μT is higher than the present-day field of 43 μT, consistent with the global data for this time-period. Most samples presented alteration during the cooling rate test, and no correction was made to these samples. Those samples on which cooling-rate correction was applied give a flow mean lower than the raw paleointensity data, as was expected.