40Ar/39Ar stratigraphy of pyroclastic units from the Caٌadas Volcanic Edifice (Tenerife, Canary Islands) and their bearing on the structural evolution

Many felsic pyroclastic units of various types are exposed in different sectors of Tenerife. New 40Ar/39Ar determinations allow them to be placed more precisely in the general volcano-stratigraphic succession. According to geographic distribution, stratigraphic position and isotopic ages, four main pyroclastic phases may be identified. The first, San Juan de la Rambla phase (2.1 Ma), is only known in the north of Tenerife in the Tigaiga massif. The second, Adeje phase (1.8–1.5 Ma), is most completely developed in the southwest of the island, but occasionally occurs in the other sectors. The third, Las Américas phase (1 Ma), is only presently known in the southern region. The fourth, Bandas del Sur phase (0.7–0.15 Ma), is essentially exposed in the southeast sector. The results of this work emphasise the complexity of the pre-1-Ma eruptive history of Tenerife and underline the fact that explosive volcanic activity has taken place for at least the last 2 Ma. Vertical collapse structures have developed as a result of pyroclastic flow activity and these may be as old as 1.6–1.8 Ma, therefore much older than generally considered. The precise location of calderas is difficult to ascertain as a result of the repeated lateral flank collapse during the construction of the Cañadas volcano.