Magma evolution of the Sete Cidades volcano, São Miguel, Azores.

Journal article
(Original article)

Publication Details

Author(s): Beier C, Hansteen T, Haase K
Journal: Journal of Petrology
Publisher: Oxford University Press (OUP): Policy B - Oxford Open Option A
Publication year: 2006
Volume: 47
Pages range: 1375-1411
ISSN: 0022-3530
Language: English


The Sete Cidades volcano (São Miguel, Azores) is situated at the eastern end of the ultraslow spreading Terceira rift axis. The volcano comprises several dominantly basaltic pre-caldera eruptions, a trachytic caldera-forming stage and a post-caldera stage consisting of alternating trachytic and basaltic eruptions. The post-caldera flank lavas are more primitive (>5 wt % MgO) than the pre-caldera lavas, implying extended fractional crystallization and longer crustal residence times for the pre-caldera, shield-building lavas. Thermobarometric estimates show that the ascending alkali basaltic magmas stagnated and crystallized at the crust-mantle boundary (∼15 km depth), whereas the more evolved magmas mainly fractionated in the upper crust (∼3 km depth). The caldera-forming eruption was triggered by a basaltic injection into a shallow trachytic magma chamber. Lavas from all stages follow a single, continuous liquid line of descent from alkali basalt to trachyte, although slight differences in incompatible element (e.g. Ba/Nb, La/Nb) and Sr isotope ratios imply some heterogeneity of the mantle source. Major and trace element data suggest similar partial melting processes throughout the evolution of the volcano. Slight geochemical differences between post- and pre-caldera stage lavas from the Sete Cidades volcanic system indicate a variation in the mantle source composition with time. The oxygen fugacity increased from the pre-caldera to the post-caldera stage lavas, probably as a result of the assimilation of crustal rocks; this is supported by the presence of crustal xenoliths in the lavas of the flank vents. The lavas from the Sete Cidades volcano generally have low Sr isotope ratios; however, rocks from one post-caldera vent on the western flank indicate mixing with magmas resembling the lavas from the neighbouring Agua de Pau volcano, having higher Sr isotope ratios. The different magma sources at Sete Cidades and the adjacent Agua de Pau volcano imply that, despite their close proximity, there is only limited interaction between them. © 2006 Oxford University Press.

FAU Authors / FAU Editors

Beier, Christoph PD Dr.
Lehrstuhl für Endogene Geodynamik
Haase, Karsten Prof. Dr.
Lehrstuhl für Endogene Geodynamik

External institutions with authors

GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel

How to cite

Beier, C., Hansteen, T., & Haase, K. (2006). Magma evolution of the Sete Cidades volcano, São Miguel, Azores. Journal of Petrology, 47, 1375-1411.

Beier, Christoph, Thor Hansteen, and Karsten Haase. "Magma evolution of the Sete Cidades volcano, São Miguel, Azores." Journal of Petrology 47 (2006): 1375-1411.


Last updated on 2018-09-08 at 12:38

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