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Quantifying the thermo-chemical evolution of magma reservoirs using mineral chemistry: a combined experimental and statistical approach
Département des sciences de la Terre Université de Genève
Institution of higher education
University of Geneva - GE
01.10.2019 - 30.09.2023
All Disciplines (3)
Experimental petrology; Dimensional reduction and clustering; Mineral chemistry; Magma reservoirs
Lay Summary (Italian)
La chimica dei minerali magmatici per comprendere i processi vulcanici a profondità inaccessibili
I magma che alimentano le eruzioni vulcaniche sono stoccati a profondità di diversi chilometri. Questo profondità sono inaccessibili tecnicamente e quindi tutte le informazioni che abbiamo sui processi magmatici che occorrono prima di un'eruzioni devo essere reperite con metodi indiretti.
I minerali che cristallizzano nei magmi registrano variazioni di temperature, pressione e chimica nella camera magmatica cambiando la loro composizione. In questo progetto faremo degli esperimenti che serviranno a tradurre il linguaggio chimico dei cristalli in variazioni di temperature, pressione e chimica dei magmi prima di un'eruzione. I risultati di questi esperimenti verranno applicati allo studio del Mt Etna, il vulcano attivo più grande d'Europa.
La zonatura chimica dei minerali ha alcune similarità con gli anelli di accrescimento degli alberi. Una differenza importante è che mentre gli alberi rimangono in un posto e registrano variazioni nella chimica del suolo e dell'atmosfera, i cristalli nei magma si muovono con traiettorie che non conosciamo a priori. Per questo utilizzeremo delle technique statistiche simili a quelle utilizzate per sequenziale il DNA per ricostruire l'evoluzione temporale delle condizioni chimico-fisiche nella camera magmatica prima di un eruzione vulcanica.
Direct link to Lay Summary
Last update: 10.07.2019
Responsible applicant and co-applicants
Département des sciences de la Terre Université de Genève
Gander Martin Jakob
Section de Mathématiques Université de Genève
The build-up to volcanic eruptions
The research we develop in my research group centres on understanding the thermal and chemical structure of subvolcanic magma reservoirs to establish the link between magmatic processes occurring at inaccessible depths, volcanic eruptions and the formation of ore deposits. This proposal is a continuation of a line of research that was initially supported three years ago. Existing analytical techniques allow us to obtain a wide variety of geochemical data from magmatic rocks, which are extremely important to gather information on the conditions of formation, transfer, storage and evolution of magmas on Earth (e.g. refs 1-9). In particular, as the chemical composition of minerals is modified by changes of melt chemistry and physical conditions of growth, profiles collected from their core to the rim allow us to trace the temporal evolution of thermal, chemical and physical conditions within magma reservoirs10-16. However, as analytical techniques are rather time consuming and expensive, detailed analyses are commonly restricted to a limited number of specimens. This limits our capability to quantify the relative proportions of minerals recording different magmatic conditions and events that occurred before eruption, thus inhibiting our capacity of reconstructing the pre-eruptive thermal and chemical architecture of magma reservoirs. To use existing analytical techniques to their full potential it is necessary to provide a framework to quantify the relative proportions of minerals recording different portions of the thermal and chemical history of magma reservoirs. This necessity is the main motivation of this project.This proposal has four main targets: 1) We will combine dimensionality reduction techniques and clustering methods to identify family of minerals (clusters) based on their core-to-rim chemistry; 2) The method will be applied to experimentally generated chemical zoned minerals to disentangle the effects of the competition between diffusion and growth of elements from chemical zoning produced by variations of the thermodynamic conditions of growth; 3) We will apply the method to clinopyroxene, olivine and plagioclase crystals of several eruptions spanning the growth history of Etna volcano to reconstruct the long-term temporal evolution of Etna’s plumbing system; 4) Combine the results obtained from different crystals for each eruption to reconstruct both the sequence of events that led to eruption and the long-term evolution of the plumbing system at Etna.In this project we will first identify and develop the most appropriate algorithms for the identification of families of mineral chemistries and then apply the method to experimentally generated (zoned) minerals and samples from Etna volcano. We tested a dimensionality reduction technique together with a clustering algorithm and obtain results from the major element characterisation of clinopyroxenes (cpx) of the Holuhraun-Bardarbunga 2014-2015 eruption and reached conclusions that are identical to those of a melt-inclusions study. Research on melt inclusions involves a significant amount of sample preparation and is analytically expensive, while the analyses of the cpx in our study were collected over a daily session at the microprobe. The approach I propose with this project can provide a powerful tool to determine on a quantitative base the chemical and physical evolution of magmatic systems.One subproject focuses on the development of the method and the establishment of the link between processes, reservoir dynamics and chemical zoning in minerals, and therefore involves a series of experiments. The experiments will be performed to produce chemically zoned minerals both in controlled static and dynamic conditions. We will use basalts from Etna volcano. The second subproject focuses on the application of our method to a natural laboratory. For this portion of the project, I selected Etna volcano because it is a well-studied system showing temporal variations of both chemistry of the erupted products and eruptive dynamics.