Análisis de la dispersión geomagnética registrada por las rocas magmáticas de Iberia durante el Jurásico y datos paleomagnéticos preliminares del volcanismo jurásico del sureste del Sistema Ibérico

Abstract

Geomagnetic field characterization is poorly known through the past. Primary magnetizations recorded in magmatic rocks are reliable, spot readings of the palaeofield and the input for palaeosecular variation of the geomagnetic field (PSV) studies, which accordingly are strongly biased to the last 5 Ma. Geomagnetic angular dispersion against the palaeolatitud is used as a measure of PSV. In this study, it is evaluated in the Jurassic period analyzing available Iberian palaeomagnetic data, focused on the Lower Jurassic Messejana-Plasencia dyke. This Iberian results are in agreement with other results from quality selected, worldwide distributed Jurassic data sets. In addition, preliminary palaeomagnetic and rock magnetic results of jurassic volcanic rocks from the southeast Iberian Range (Spain) are reported. Sampled units consist of volcanoclastic materials (3 sites) and basaltic lava flows (5 sites) from the Sierra de Javalambre of around Toarcian-Aalenian ages. Two directional components were sometimes observed in the basaltic rocks, the high-temperature component showing both normal and reversed polarities and therefore being considered as the Characteristic Remanent Magnetization (ChRM). The ChRMs are assumed to be acquired before the tectonic deformation of this area and they are analyzed after their palaeohorizontal restitution. Despite the presence of north oriented (before tilt correction) normal polarities recorded by the volcanoclastic rocks, it is statistically argued that there is no reason to discard a primary origin for all the 8 site mean ChRM directions. More palaeomagnetic results from these both magmatic lithologies from the southeast Iberian Range will be welcomed for further geodynamic and geomagnetic interpretations. Javalambre data set is still relatively scattered and not large enough to conform to a Virtual Geomagnetic Poles (VGPs) distribution representative of the time averaged geomagnetic palaeofield. This fact is highlighted when this study results are compared with both the Jurassic palaeolatitud data set available for Iberia and with the geomagnetic dispersion obtained from the Messejana-Plasencia dyke and from worldwide distributed Jurassic data sets.