Composición y evolución de las lavas de la isla de Branco (Cabo Verde)

Abstract

The first data about the composition of lava flows from Branco Island (Cabo Verde) are presented in this
work. Most lava flows in the sequence are alkali basalts (Fo84-76 olivine, En44-36 diopside, An83-31 plagioclase)
showing geochemical affinity of typical ocean island basalts. The scarce most evolved members are
mugearites (olivine absent, En41-31 clinopyroxene, An51-26 plagioclase, and kaersutite). The compositional
variations between both the types are explained by crystal fractionation and extraction of pyroxene (up to
29%) and lesser proportions of olivine and Fe and Ti oxides (Cpx: 75; Ol: 21; OxFeTi: 4). The transition to
mugearites from the most evolved basalts would mainly be due to extraction of pyroxene (24%) and Fe
and Ti oxides (Cpx: 68; Ol: 3; Plag: 5; OxFeTi: 30).