GEOLOGÍA, PETROGRAFÍA Y EDAD U-PB DE UN ENJAMBRE LONGITUDINAL NO-SE DE DIQUES DEL MACIZO NORDPATAGÓNICO ORIENTAL, RÍO NEGRO

In this contribution we review the stratigraphic relationships and petrography of a longitudinal NW-SE dyke swarm, in a broad sector of Eastern Northpatagonian Massif (Rio Negro). Also a U-Pb age on zircon is presented as the crystallization age of these dikes. The swarm extends in NW direction for about 100 km long, between Punta Porfido and Rincon de Paileman, and in a belt about 35 km wide. Its composition is essentially andesitic-traquiandesitic, showing internal variations of the distribution of subvolcanic textures produced by different thermal cooling histories. The stratigraphic relationships of the swarm with their host rocks and the U-Pb age of 243 Ma indicate that it belongs to a postorogenic event of the permian Gondwanic Cycle and is previous to the volcanic and pyroclastic rocks of the Marifil Volcanic Complex. The dikes are hosted in the same NW structures than the intrusive and extrusive bodies of the mentioned complex. The swarm has a regional distribution to the east of the Northpatagonian Massif and is a transitional igneous event between the permian Gondwanic magmatic activity and the Marifil Volcanic Complex.