Geocronología de las rocas volcánicas de El Castillo (Salamanca, Zona Centroibérica)

Abstract

Exposures of volcanic rocks (El Castillo) in the Central Iberian Zone near Salamanca, Spain, are representativeof Paleozoic volcanic activity along the northern Gondwanan passive margin. Alkaline basalts and maficvolcaniclastic rocks of this sequence are structurally preserved in the core of the Variscan Tamames Syncline.On the basis of the occurrence of graptolite fossils in immediately underlying strata, the El Castillo volcanicstraditionally have been regarded as Lower Silurian in age. In contrast, most Paleozoic volcanic units in westernIberia are rift-related mafic to felsic rocks emplaced during the Late Cambrian-Early Ordovician, and areattributed to the opening of the Rheic Ocean. We present new zircon U-Pb TIMS data from a mafic volcaniclasticrock within the El Castillo unit. These data yield a near-concordant, upper intercept age of 394.7 ± 1.4 Mathat is interpreted to reflect a Middle Devonian (Emsian-Eifelian) age for the magmatism, demonstrating thatthe El Castillo volcanic rocks lie unparaconformably above lower Silurian strata.