The Holocene volcanism at El Hierro: insights from petrology and geochemistry

Abstract

The Holocene volcanism at El Hierro consists of basaltic monogenetic volcanic fields associated with o the three rift systems present in this island. In this work we report preliminary petrological and geochemical data of Holocene lava flows belonging to the WNW-striking rift. Sampling was focused in three zones: Orchilla, Verodal-Sabinosa, and Tanganasoga. Petrography of the studied lavas shows that they are homogeneous. All samples are porphyritic with macrocrysts of clinopyroxene and olivine immersed in a groundmass formed by microcrysts of plagioclase, Fe-Ti oxides and clinopyroxene. Clinopyroxenes are diopsides, olivines have forsterite contents ranging from 74 to 84 % and anorthite in plagioclase varies from 66 to 76% (labradorite). Whole-rock geochemical results evidence that all magmas are basic in composition, ranging from picrobasalts to phonotephrites. Major, trace elements and isotope support fractional crystallization as the main process of magma evolution. However, petrography and chemistry of clinopyroxene cores agree with a xenocrystic nature of some of them. We suggest that these clinopyroxene cores crystallized from a genetically related magma and subsequently were entrapped or cannibalized by the basic rising magmas.