Identificador persistente para citar o vincular este elemento: http://hdl.handle.net/10553/48698
Título: Low-temperature hydrothermal alteration of intra-caldera tuffs, Miocene Tejeda caldera, Gran Canaria, Canary Islands
Autores/as: Donoghue, Eleanor
Troll, Valentin R.
Harris, Chris
O'Halloran, Aoife
Walter, Thomas R.
Torrado, F. J. Perez 
Clasificación UNESCO: 250621 Vulcanología
Palabras clave: Hydrothermal alteration
Stable isotopes
Tejeda caldera
Gran Canaria
Canary Islands
Fecha de publicación: 2006
Publicación seriada: Geochimica et Cosmochimica Acta 
Conferencia: 16th Annual V.M. Goldschmidt Conference 
Resumen: The Miocene Tejeda caldera on Gran Canaria erupted ~ 20 rhyolite–trachyte ignimbrites (Mogán Group 14–13.3 Ma), followed by ~ 20 phonolitic lava flows and ignimbrites (Fataga Group 13–8.5 Ma). Upper-Mogán tuffs have been severely altered immediately within the caldera margin, whereas extra-caldera Mogán ignimbrites, and overlying Fataga units, are apparently unaltered. The altered intra-caldera samples contain minerals characteristic of secondary fluid–rock interaction (clays, zeolites, adularia), and relics of the primary mineral assemblage identified in unaltered ignimbrites (K-feldspar, plagioclase, pyroxene, amphibole, and groundmass quartz). Major and trace-element data indicate that Si, Na, K, Pb, Sr, and Rb, were strongly mobilized during fluid–rock interaction, whereas Ti, Zr, and Nb behaved in a more refractory manner, experiencing only minor mobilization. The δ18O values of the altered intra-caldera tuffs are significantly higher than in unaltered extra-caldera ignimbrites, consistent with an overall low-temperature alteration environment. Unaltered extra-caldera ignimbrites have δD values between − 110‰ and − 173‰, which may reflect Rayleigh-type magma degassing and/or post-depositional vapour release. The δD values of the altered intra-caldera tuffs range from − 52‰ to − 131‰, with ambient meteoric water at the alteration site estimated at ca. − 15‰. Interaction and equilibration of the intra-caldera tuffs with ambient meteoric water at low temperature can only account for whole-rock δD values of around − 45‰, given that ∆Dclay–water is ca. − 30‰ at 100 °C, and decreases in magnitude at higher temperatures. All altered tuff samples have δD values that are substantially lower than − 45‰, indicating interaction with a meteoric water source with a δD value more negative than − 15‰, which may have been produced in low-temperature steam fumaroles. Supported by numerical modeling, our Gran Canaria data reflect the near-surface, epithermal part of a larger, fault-controlled hydrothermal system associated with the emplacement of the high-level Fataga magma chamber system. In this near-surface environment, fluid temperatures probably did not exceed 200–250 °C.
URI: http://hdl.handle.net/10553/48698
ISSN: 0016-7037
DOI: 10.1016/j.gca.2006.06.304
Fuente: Geochimica Et Cosmochimica Acta [ISSN 0016-7037], v. 70 (Supplement 18), p. A144
Colección:Actas de congresos
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