Registro magnético de la paleotectónica de los Plutones de María Madre y Puerto Vallarta (Cretácico Superior, México)

Resumen

In this study we examine the magnetic record of late-Cretaceous, coeval (~80-90 Ma) granitic rocks from the Mexican Pacific coastal plutonic belt (at the southern continental margin of the Gulf of California oblique rift system) and its suitability for paleotectonic purposes. These rocks (26 sites, ~200 individually oriented samples) were collected in fresh outcrops from the Puerto Vallarta Batholith (PVB; around Bahía de Banderas, Jalisco) and in the María Madre Island (MM; located ~150 km NW of Bahía de Banderas). Different rock magnetic experiments, optic inspections, anisotropy of magnetic susceptibility (AMS) analysis, and remanence measurements after thermal and alternating-field detailed demagnetization have been performed in specimens from both plutons. These plutons record ancient, dual-polarity geomagnetic field components (faraway of recent directions but sometimes partially overlapped with them). Magnetite is the unique magnetic carrier, ubiquitous in a wide range of predominantly large grain volumes. We discuss here the tectonic significance of paleomagnetic directions, magnetic fabric data and AMS directions accordingly to the former ones. Lineations and foliation planes from the MM pluton show dissimilar results to those from the PVB in which a more complex tectonic control of the AMS is suggested.