Petrology and geochemistry of the Bandas del Sur Formation, Las Canadas Edifice, Tenerife (Canary Islands)

Bryan, S. E., Marti, J. and Leosson, M. (2002) Petrology and geochemistry of the Bandas del Sur Formation, Las Canadas Edifice, Tenerife (Canary Islands). Journal of Petrology, 43 10: 1815-1856. doi:10.1093/petrology/43.10.1815

Author Bryan, S. E.
Marti, J.
Leosson, M.
Title Petrology and geochemistry of the Bandas del Sur Formation, Las Canadas Edifice, Tenerife (Canary Islands)
Journal name Journal of Petrology   Check publisher's open access policy
ISSN 0022-3530
Publication date 2002-10
Sub-type Article (original research)
DOI 10.1093/petrology/43.10.1815
Volume 43
Issue 10
Start page 1815
End page 1856
Total pages 42
Editor M. Wilson
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Collection year 2002
Language eng
Subject C1
260102 Igneous and Metamorphic Petrology
780104 Earth sciences
Abstract The Bandas del Sur Formation preserves a Quaternary extra-caldera record of central phonolitic explosive volcanism of the Las Canadas volcano at Tenerife. Volcanic rocks are bimodal in composition, being predominantly phonolitic pyroclastic deposits, several eruptions of which resulted in summit caldera collapse, alkali basaltic lavas erupted from many fissures around the flanks. For the pyroclastic deposits, there is a broad range of pumice glass compositions from phonotephrite to phonolite. The phonolite pyroclastic deposits are also characterized by a diverse, 7-8-phase phenocryst assemblage (alkali feldspar + biotite + sodian diopside + titanomagnetite + ilmenite + nosean-hauyne + titanite + apatite) with alkali feldspar dominant, in contrast to interbedded phonolite lavas that typically have lower phenocryst contents and lack hydrous phases. Petrological and geochemical data are consistent with fractional crystallization (involving the observed phenocryst assemblages) as the dominant process in the development of phonolite magmas. New stratigraphically constrained data indicate that petrological and geochemical differences exist between pyroclastic deposits of the last two explosive cycles of phonolitic volcanism. Cycle 2 (0.85-0.57 Ma) pyroclastic fall deposits commonly show a cryptic compositional zonation indicating that several eruptions tapped chemically, and probably thermally stratified magma systems. Evidence for magma mixing is most widespread in the pyroclastic deposits of Cycle 3 (0.37-0.17 Ma), which includes the presence of reversely and normally zoned phenocrysts, quenched mafic glass blebs in pumice, banded pumice, and bimodal to polymodal phenocryst compositional populations. Syn-eruptive mixing events involved mostly phonolite and tephriphonolite magmas, whereas a pre-eruptive mixing event involving basaltic magma is recorded in several banded pumice-bearing ignimbrites of Cycle 3. The periodic addition and mixing of basaltic magma ultimately may have triggered several eruptions. Recharge and underplating by basaltic magma is interpreted to have elevated sulphur contents (occurring as an exsolved gas phase) in the capping phonolitic magma reservoir. This promoted nosean-hauyne crystallization over nepheline, elevated SO3 contents in apatite, and possibly resulted in large, climatologically important SO2 emissions.
Keyword Tenerife
Crystal Fractionation
Magna Mixing
Sulphur-rich Explosive Eruptions
Geochemistry & Geophysics
Magma Mixing
Magma Bodies
Fractional Crystallization
Alkaline Magmas
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Earth Sciences Publications
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Created: Tue, 14 Aug 2007, 17:37:27 EST