Basanite-Phonolite Lineages of the Teide-Pico Viejo Volcanic Complex, Tenerife, Canary Islands

Abstract

The petrology, geochemistry and petrogenesis of the active Teide–Pico Viejo volcanic complex provide information about the evolution and internal structure of the Tenerife central magma system during its most recent volcanic cycle. Two petrologically distinct basaniten–phonolite lineages are identified, which correlate essentially with the products of the Pico Teide and Pico Viejo stratovolcanoes. Geochemical modelling supports the evolution of both series from a common evolved basanite parent, by crystal fractionation under different physico-chemical conditions. Pico Viejo series intermediate magmas fractionated mainly kaersutite and low-Or plagioclase at high PH2O, whereas Teide series examples fractionated mainly high–Or plagioclase and clinopyroxene at low PH2O, resulting in lower Ba, Sr, Eu/Eu* and MREE/HREE, and less peralkaline phonolitic residua. The Pico Viejo series shows smooth modal, mineralogical and whole-rock chemical variations, whereas the Teide series shows the additional effects of mineral accumulation, magma mixing, assimilation of hydrothermally altered crust and contamination by felsic magmas. Pyroxene barometry suggests that parental basanites and Pico Viejo series intermediate magmas evolved in the lower crust and uppermost mantle at 6–12 kbar Ptotal. Teide series intermediate magmas experienced polybaric fractionation, also differentiating extensively within a shallow chamber beneath Teide, where low PH2O conditions resulted from low Ptotal and, on the basis of F and Cl systematics, from open–system degassing. Hygrometry and melt-inclusion data from phonolites suggest a shallow Teide chamber at ∼1.5 kbar Ptotal, whereas Pico Viejo series phonolites evolved in a separate shallow chamber at ∼1 kbar Ptotal.