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Abstract

The Central Vólcanic Complex I (CVC-I) consists maihly of mildly alkaline basalts, many of them ankaramitic. The compositional differences observed are explained by fractíonation and extraction (rates between 20% and 30%) of clinopyroxene (60%), olivine (20-25%) and titanomagnetite. The CVC-II shows two different stages. The lower one of mildly alkaline affiníty has an age comprised between 20 and 22 Ma, the more alkalic: upper orle has a mote recent age about 18Ma. The crystallization models for the lower stage are different depending on the composition considered to be the most primary or less differentiated magma. The crystallization rates are comprised between 20 and 30%. The compositional variation observed in the basalts from the upper stage may be due to crystallization rates from 20-25%, mainly olivine (50c70%) and clinopyroxene. The transition to trachyandesites, both in the CVC-I and the CVC-II¡ supposes a change in crystallization which is then dominated by cilinopyroxene and plagioclase. The further transition to trachytes is a process controlled by plagioclase extraction.