Ana C. Lossada, Augusto E. Rapalini y Leda Sánchez Betucci
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Revista de la Asociación Geológica Argentina,vol.71 no.3 Buenos Aires set. 2014
El enjambre de diques básicos de Nico Pérez-Zapicán intruye al basamento paleoproterozoico del cratón del Río de la Plata en las cercanías de las localidades homónimas, departamento de Lavalleja, Uruguay. A partir de la identificación y el mapeo de detalle de la ubicación de los distintos diques, su descripción petrográfica, y de los estudios geocronológicos, paleomagnéticos y de magnetofábrica realizados en la unidad, se pudo caracterizar de manera más acotada su geología y su contexto temporal. Los diques presentaron una remanencia magnética estable, considerada primaria, que permitió calcular el polo paleomagnético del enjambre de diques básicos de Nico Pérez, el cual se ubica en 87ºS; 197,3ºE (A95=10,2º, n=8, k=30), y es consistente con la posición de otros polos de referencia de América del Sur entre el Jurásico Medio y el Jurásico Superior. La petrofábrica, caracterizada mediante un estudio de anisotropía de susceptibilidad magnética, resultó ser de origen magmático, encontrándose fábricas normales e inversas. La elevada inclinación observada en la lineación magnética sugiere que el flujo magmático en los diques fue subvertical al momento de la intrusión. El estudio geocronológico basado en una datación por el método 39Ar/40Ar sobre plagioclasa arrojó una edad de 157,6±3,0 Ma para la intrusión de los diques. En función de las evidencias geocronológicas, petrográficas y paleomagnéticas expuestas en este trabajo, se postula que el evento que dio lugar a la intrusión del enjambre de diques básicos de Nico Pérez-Zapicán ocurrió en el Mesozoico, probablemente asociado a los primeros esfuerzos distensivos que culminaron con la apertura del océano Atlántico Sur.
Palabras clave: Diques básicos; Cratón Río de la Plata; Paleomagnetismo; Uruguay.
Palabras clave: Diques básicos; Cratón Río de la Plata; Paleomagnetismo; Uruguay.
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 an 39Ar/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.
Keywords: Basic dykes; Río de la Plata craton; Paleomagnetism; Uruguay.
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 an 39Ar/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.
Keywords: Basic dykes; Río de la Plata craton; Paleomagnetism; Uruguay.
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