El volcanismo alcalino pre-hercinico del sinclinal de Almadén

Abstract

In the Almadén region an important volcanic activity of Devonian age took place. It began in the Emsian in the central part of the syncline, and was developed in several consecutive episodes along the Frasnian. Intense postmagmatic deuteric or hydrothermal processes have generated a low-temperature mineralogical assemblage resembling the spilite-keratophyre association. Hence, the volcanism in the Almadén region is characterized, using minor and trace elements considered to be inmovile (Ti, Zr, Y, Nb and partly, P and Ga). We conc1ude the existence of a mildly alkaline primitive magma, place below an oceanic or transitional crust in a within-plate setting; later differentiation may have taken place by fractional crystallization.