Resumen de El Piroxeno de las rocas volcánicas miocenas de la isla de Fuerteventura (Islas Canarias).
José Luis Brandle Matesanz, Eumenio Ancochea Soto, María José Huertas Coronel, C. R. Cubas, Francisco Hernán Reguera
Pyroxene (diopside or augite) is present in al/ rocks of the Miocene Volcanic Complexes on Fuerteventura. Pyroxene phenocrysts are specially abundant in basa/ts, in which they represent a third of al/ phenocrysts. The En/(En + Fs) ratio decreases from core to rim in the scarce zoned phenocrysts and is a/ways Jower in the sma/1 crystals forming the groundmass. The En-content is a/so e/ose/y re/ated to the total-rock weight percent MgO. The variation in a rock sample is, sometimes, as large as the one observed as a whole. The total range is En85_69 in basalts, En81_63 in trachybasa/ts, En77_64 in basa/tic trachyandesites, En74_68 in trachyandesites and En70_62 in trachytes. The maximum En-content of basalts remains constant regard/ess the rock MgO concentration. This is due to crystallisation of pyroxene after an important amount of o/ivine, when the residual liquid is strongly Mg-depleted.The Ca+Na - Ti concentrations are those typica/ of a/kaline rocks, showing an evident increase in Wo-component With increasing rock alkalinity. The Wo-component decreases from phenocrysts to groundmass in mildly a/kaline rocks, remains constant in middle a/kaline rocks and increases in strongly alkaline and ultra-alka/ine rocks.
