Comprehensive Paleomagnetic Study of the Oligocene-Miocene Rocks from the San Luis Potosí Volcanic Field, Mexico

Abstract:

Comprehensive paleomagnetic study of the Oligocene-Miocene sequence of lithological units from the San Luis Potosí volcanic field in central Mexico was accomplished to set up the magnetostratigraphic record. Two hundred and one oriented standard paleomagnetic cores corresponding to twenty-eight paleomagnetic sites were collected from all units. Rock-magnetic properties are characteristic for each unit. Isothermal remanent magnetization acquisition curves and continuous susceptibility vs. temperature experiments point from low to medium-Ti content in titanomagnetite as the main opaque magnetic minerals, presumably result from oxy-exsolution processes during the initial flow cooling. Opaque mineral microscopy supports this assumption. Unblocking temperature and hysteresis parameters suggests predominance of pseudo-single domain magnetic grain size. Thermal and alternating field demagnetizations show mostly well-defined univectorial magnetizations. Most sites present a mean direction with small angular dispersion. 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 dipolar value for the locality. Anisotropy of magnetic susceptibility lineation match the geologically inferred flow direction.