| Summary: | Nico Pérez-Zapicán basic dykes swarm, Uruguay: radimetric and paleomagnetic evidence about their age The Nico Pérez-Zapicán basic dykes swarm intrudes the Paleoproterozoic basement of the Río de la Plata craton in the vecinity of the homonimous towns, Lavalleja department, Uruguay. From the identification and detailed mapping of the dykes, petrographic descriptions, and geochronologic, paleomagnetic and magnetofabric analysis, it was possible to characterize their geologic characteristics and temporal context in a more accurate way. Dykes present a high stability remanence, considered to be primary, which allowed us to calculate the Paleomagnetic Pole of the Nico Pérez basic dykes swarm, which is located at 87ºS; 197,3ºE (A95=10,2º, n=8, k=30,31), and is consistent with other reference poles of South America from middle to upper Jurassic. The petrofabric of the dykes was characterized by an analysis of the anisotropy of magnetic susceptibility, which resulted to be of magmatic origin. Normal and reverse fabrics were observed. The geochronologic analysis, based on an39Ar/40Ar dating on plagioclase, yielded a 157,6±3,0 Ma age for the intrusion of the dykes. Taking into account the geochronologic, petrographic and paleomagnetic evidence exposed in this work, we propose that the event that originated the intrusion of the Nico Pérez basic dykes swarm took place in Mesozoic times, probably associated with first tensional stresses that preceded the opening of the South Atlantic Ocean. © 2014, Asociacion Geologica Argentina. All rights reserved.
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