Edad U-Pb en monacitas y rútilos de los paragneises de la Unidad de Agualada (Complejo de Ordenes, NW del Macizo Ibérico)

Abstract

The Agualada Unit is a small (3x5 km) tectonic slice of the lowermost allochthon of the Órdenes Complex. It is mainly formed by orthogneisses, migmatitic paragneisses and numerous mafic lenses. The nature of the lenses vary from well preserved eclogites to highly retrogressed garnet amphibolites and reflect peak eclogitic conditions ofT » 720 °C and P > 15 kbar. The partial melting of the paragneisses, simultaneous with the development of the regional foliation, is related to decompresion and took place under amphibolite-facies conditions. This is evidenced because the regional fabric sometimes penetrates the rims of the mafic lenses producing intense amphibolitization and transposition of the previous syn-eclogitic foliation. Monazites and rutiles from the paragneisses have been dated at 346 ± 2 Ma and 341 ± 3 Ma, respectively. These ages are interpreted as the age of migmatization (monazites) and a subsequent rapid cooling (rutiles)