Contributions to the chronology of the Basal Complex of Fuerteventura, Canary Islands

K-Ar and Ar-Ar analyses of the Basal Complex of Fuerteventura confirm the e arly start of magmatism in the Late Cretaceous. Plateau ages of 63.1 +/- 0. 8 Ma and 64.2 +/- 1.0 Ma have been obtained for the oldest syenite intrusio ns indicating the minimum age of these plutonics. The emplacement of carbon atites and syenites along ductile shear zones took place during a relativel y short period of time between 23.2 +/- 1.0 and 22.1 +/- 0.9 Ma. This episo de is synchronous all over the island. Younger plutons were intruded around 21.1 +/- 0.8 Ma ago and 20.7 +/- 0.9 Ma and are probably related to the bu ilding of Miocene subaerial edifices. Almost all the minerals and rocks of the Basal Complex show a clear effect of excess argon. Some was acquired du ring the hydrothermal stage but also some excess argon was trapped during t he early crystallization stage of the magma. Moreover, only a part of the r adiogenic Ar which had accumulated in pre-Miocene rocks was released during the Miocene magmatism. (C) 1999 Elsevier Science B.V. All rights reserved.