Aspectos composidonales de los piroxenos ígneos del magmatismo básico del sinclinal de Almadén. Implicaciones petrogenéticas

Abstract

Chemical composition of igneous pyroxenes in the basic rocks from the Almadén syncline shows important differences between basaltic lavas and olivine diabases (Silurian to Devonian in age), and quartzdiabases on the other hand. Higher CaO, Al203 and Ti02 and lower Si02 contents in pyroxenes from the first group are characteristics of alkaline magmas. Lower CaO, Al203 and Ti02 and higher Si02 in pyroxene from quartzdiabases are indicative of a subalkaline (tholeiitic) affinity. These chemical differences are consistent with whole-rock chemistry, with higher Nb/Y and (La/Lu)cn ratios in the first group. Alkaline and tholeiitic magmatism are a consequence of different partial melting rates, lower for the alkaline liquids