Resumen de Preliminary apatite-fission track geochronology of the Montaña BlancaMilocho, alkaline pluton, (NW Fuerte ventura, Canary Islands, Spain)

Cristina de Ignacio San José, M. Muñoz, J. Sagredo, Luis C. Barbero González

• The mafic-ultramafic, alkaline Montana Blanca-Milocho pluton, which is part o f the northernmost outcrop of the Basal Complex of the island of Fuerteventura, Canary Islands, is spatially associated to the Jablitos alkaline-carbonatitic complex. Alkaline clinopyroxenites occurring in the periphery o f both intrusive bodies bear strong petrographic, mineralogical and geochemical similarities. However, the study o f a possible genetic relationship between them was so far hindered by the complete absence of geoclironological data. High apatite abundances in these rocks has allowed the application o f the fission track techniques as a geoclironological tool. Nevertheless, in samples were perovskite occurs the lack o f U in apatite, the K-Ar method had to be used. The 25 and 29 Ma fission tracks central ages obtained are well in agreement with theexpected emplacement age o f these shallow intrusive rocks, and also with published and new K-Ar ages.

  Thus, a genetic relationship between these ultramafic alkaline clinopyroxenites is here proposed.