An integrated paleomagnetic and multispecimen paleointensity study from the late Jurassic Zapicán dike swarm (Uruguay)

Abstract

A rock magnetic, paleomagnetic and absolute intensity study was conducted on 21 basic dike swarms situated in the Zapicán area (Lavalleja, Uruguay). Paleomagnetic directions revealed mostly normal polarity magnetizations with few intermediate and reverse polarity dikes. Combining data from a previous study, a mean paleodirection obtained is Dec = 3.5°, Inc = −50.6°, α95 = 6.3°, N = 19, corresponding to a paleomagnetic pole PLat = 86.4° S, PLong = 178.9° E, A95 = 7.2°. This pole position coincides, within uncertainties, with other poles proposed for the same region and age. The paleomagnetic intensities obtained by the multispecimen method including fraction and domain state corrections yielded values from 13.4 to 66.5 μT (and from 2.5 to 12.4 1022 Am2 in terms of virtual axial dipole moments). This indicates that the geomagnetic field probably experienced relatively high fluctuations at the end of the Jurassic Hyperactivity Period (more than 10 reversals per million years) questioning the relationship between the strength of the geomagnetic field and reversal rate.