The Esquinzo Ultra-Alkaline Rock Suite of Fuerteventura Basal Complex (Canary Islands): Evidence for Origin of Carbonatites by Fractional Crystallization

Abstract

The origin of the carbonatites that appear on Earth is one of the most controversial current topics in the petrogenesis of igneous rocks. Situated in the northern sector of the Basal Complex of Fuerteventura (Canary Islands), the Miocene Esquinzo ultra-alkaline plutonic rock complex is composed of pyroxenites, melteigites-ijolites-urtites, malignites-nepheline syenites, carbonatites, silicocarbonatites, nephelinites and nepheline phonolites. This work tries to establish the genesis of this massif of ultra-alkaline rocks with associated carbonatites from Fuerteventura (which are very rare in the oceans). The geochemical characteristics of these rocks and the minerals that are included in them have allowed us to establish their origin. This complex was generated by three successive magmatic events associated with differentiation of melanephelinite magmas emplaced in the oceanic crust. Silicocarbonatite and calciocarbonatite (sövites) dykes are related to the first magmatic event and were formed by fractional crystallization of H2O- and CO2-rich ijolite magmas. The melanephelinite magmas that formed these plutonic ultra-alkaline rocks were apparently generated as partial melts of asthenospheric mantle, which assimilated enriched lithospheric mantle material as they ascended. The upwelling of this large body of anomalous asthenospheric Miocene material exceeded the deformation associated with plate motions and led to an oceanic rifting event in Fuerteventura.