Controls of magma chamber zonation on eruption dynamics and deposits stratigraphy: The case of El Palomar fallout succession (Tenerife, Canary Islands)

Joan Martí,Silvia Zafrilla,Joan Andújar,María Jiménez-Mejías,Bruno Scaillet,Dario Pedrazzi,Domenico Doronzo,Stephane Scaillet

doi:10.1016/j.jvolgeores.2020.106908

Abstract

Anticipating volcanic eruptions at central volcanoes require knowing how magma chambers prepare for new eruptions. Pre-eruptive processes that occur in such magma chambers are recorded in the products of these eruptions, so their characterisation in terms of magma composition and physics offers the clues to understand past eruptions and predict future ones. Here, we study the very well preserved pyroclastic succession of El Palomar Member (712 ± 41 ka), in Las Cañadas caldera, Teide, Canary Islands. This deposit resulted from a single explosive eruption of a phonolitic magma that started with a sustained eruption column (sub-plinian or plinian) that formed a massive, 40 m thick non-welded fallout deposit, progressively changing into a lower intensity fire fountain that deposited a 25 m thick fallout succession of non-welded to strongly welded pumices. Stratigraphic and petrological data suggest that this eruption was related to a thermally-compositionally zoned and relatively shallow magma chamber in which the arrival of a hotter and more mafic magma rapidly triggered the eruption. The studied deposit shows how this zoned structure was maintained during the whole process, which allows one to reconstruct what happened during the eruption. Comparison of this eruption with the current situation at Teide volcano alerts on the potential rapid preparation for new eruptions in the case that sufficient phonolitic magma was available in the shallow plumbing system of this active volcano if new inputs of deeper magma take place.

Highlights

A good knowledge of the formation and dynamics of magma chambers is crucial to understanding how magmas evolve and how they subsequently erupt at the Earth’s surface
In this work we focus on the Las Cañadas caldera, in Tenerife, which was generated by several caldera-forming eruptions of phonolitic magmas (Martí et al, 1994; Martí and Gudmundsson, 2000; Martí, 2019)
On the light of the data presented above, we can discuss on whether the physicochemical variations observed in stratigraphic succession of the El Palomar Member reflect changes existing in the magma chamber prior to eruption, or respond to processes occurring in the eruptive conduit, or both

Summary

Introduction

A good knowledge of the formation and dynamics of magma chambers is crucial to understanding how magmas evolve and how they subsequently erupt at the Earth’s surface. Some other deposits show different compositional patterns including abrupt gaps in composition between the erupted products (e.g., Bacon and Druitt 1988), or lack of any compositional gradients (Lindsay et al, 2001; Bachmann et al, 2002), suggesting that either there was no zonation in the pre-eruptive magma chamber or that processes such as mixing or convection occurred prior to, or during, the eruption, disturbing any existing zonation Deciphering these processes, which may occur prior to the eruption and during it, from the erupted products is important to understand eruption dynamics and how magmas prepare to erupt. Important is to distinguish the processes that occur in the magma chamber from those that may occur in the eruptive conduit and that may overprint the first ones (e.g., Freundt and Tait, 1986; Koyaguchi, 1987)

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