Pre-Eruptive Conditions and Dynamics Recorded in Banded Pumices from the El Abrigo Caldera-Forming Eruption (Tenerife, Canary Islands)

Author:

González-García Diego12,Petrelli Maurizio3,Perugini Diego3,Giordano Daniele14,Vasseur Jérémie5,Paredes-Mariño Joali36,Marti Joan7,Dingwell Donald B5

Affiliation:

1. Dipartimento di Scienze Della Terra, Università degli Studi di Torino, via Valperga Caluso 35, 10135 Turin, Italy

2. Institut für Mineralogie, Leibniz Universität Hannover, Callinstrasse 3, 30167 Hannover, Germany

3. Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Piazza Università 1, 06123 Perugia, Italy

4. Istituto di Geoscienze e Georisorse, (IGG), Centro Nazionale delle Ricerche (CNR), Area della Ricerca di Pisa San Cataldo, 56124 Pisa, Italy

5. Department für Geo- und Umweltwissenschaften, Ludwig-Maximilians-Universität München, Theresienstr. 41/III, 80333 Munich, Germany

6. School of Environment, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand

7. Geosciences Barcelona (GEO3BCN-CSIC), C/ Lluis Solé i Sabarís, s/n, 08028 Barcelona, Spain

Abstract

Abstract The El Abrigo member of the Diego Hernández Formation (Tenerife, Canary Islands) represents the final (170 ka) and most voluminous eruption (>20-km3 DRE) of the last cycle of explosive activity of the Las Cañadas volcano. It is a dominantly phonolitic ignimbrite containing both mafic and banded pumices, suggesting that magma mixing played an important role in triggering the eruption and modulating eruptive dynamics. Here we use petrology, together with glass and mineral geochemistry of enclave-rich mafic scoriae, banded and phonolitic pumices from El Abrigo ignimbrite, to shed light on the pre-eruptive storage conditions and processes governing magma ascent and interaction dynamics and to provide a first-order assessment of the contribution of magma mixing and crystal mush melting to the dynamics of this eruptive event. The distribution of major elements in glasses is consistent with diffusive exchange between the interacting melts whereby Na transfers from the phonolite to the tephriphonolitic melt. However, V, Zr, Ba, and Eu suggest a complex scenario in which an intruding tephritic to phonotephritic magma interacted with two distinct zones of a phonolitic magma chamber, one occupied by a crystal-rich, low-Zr, and high-Ba phonolite, and the other by an evolved, crystal-poor, high-Zr phonolite. These results, coupled with mineral–melt thermobarometry, allow us to reconstruct the Las Cañadas plumbing system at the end of the Diego Hernández cycle and to evaluate the contribution of cumulate mush melting and magma mixing in as follows: (1) the parental tephritic magma was stored at or near the Moho (410–450 MPa) at 1050°C where it was periodically replenished by more primitive basanitic magma; (2) upon ascent, the tephrite intruded into a shallow and zoned phonolitic storage system, triggering the disruption of a crystal mush in its base; and (3) subsequently interacted with a crystal-poor zone within the reservoir. Energy balance evaluations suggest that relative mafic magma volume ratios ranged from 20 to 43 vol%, and the conservation of small-scale magma mingling structures and their geochemical distribution suggest that the mixing event took place very shortly before the eruption, on a timescale of hours.

Publisher

Oxford University Press (OUP)

Subject

Geochemistry and Petrology,Geophysics

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