Anorthite-calibrated backscattered electron profiles, trace elements, and growth textures in feldspars from the Teide–Pico Viejo volcanic complex (Tenerife)

Abstract

Magma chamber dynamics at the phonolitic to basanitic Teide–Pico Viejo volcanic complex on Tenerife, Canary Islands, have been investigated using feldspar zonation and chemistry. Backscattered electron-image grey value profiles, obtained by electron microprobe and calibrated on anorthite content, allow the investigation of much better spatially resolved zonation profiles than quantitative point analysis alone. On the basis of these zonation patterns and trace element analyses by electron microprobe, magma chamber processes such as magma recharge and mingling, as well as whole-chamber overturn events, can be identified and characterized in more detail. Samples from all investigated eruption centres contain feldspars, which have experienced growth in a deep reservoir, followed by ascent, resorption, and growth of mantles in more shallow levels in the crust just prior to eruption. Two Pico Viejo samples exhibit feldspars with a characteristic drop in anorthite content, which is not accompanied by resorption. Trace element behaviour in these samples shows that cores and mantles have grown from the same magma reservoir: The conclusion from these data is that there occurred complete overturn events in layered magma chambers, presumably induced by cold plumes from the cupola layers. A mass balance calculation shows that the proportions of the layers are ∼ 75 wt.% lower part and ∼ 25 wt.% cupola layer. Correlations between zonation patterns of single crystals in different rocks show that the Teide magma chambers are larger and chemically buffered compared with the smaller Pico Viejo system. Feldspars from Pico Viejo exhibit rather complex anorthite-profiles and more frequently display disturbances likely to be caused by arrival of new magma batches.