Amphibole: a mineral to unravel magma storage and timescales of sub-volcanic processes and eruptions

Amphibole: a mineral to unravel magma storage and timescales of sub-volcanic processes and eruptions

Leitung:  Dr. Filippo Ridolfi
Team:  eigene Stelle
Jahr:  2019
Förderung:  DFG
Laufzeit:  2019-2021

Amphibole is a very versatile mineral, as it plays a crucial role in the study of several earth and planetary processes. One of its most common applications is geothermobarometry, especially in volcanic systems, whereas it has never been used to constrain the timescales of subvolcanic processes (within its P-T stability field) and of the most violent eruptions (e.g. Plinian). This project aims to (1) improve the accuracy of thermobarometric determinations using Mg-rich calcic amphiboles which are typical for calcalkaline and alkaline melts (subduction-related and intraplate volcanism), (2) investigate textural and compositional variations of amphibole as a function of cooling and decompression rates and (3) unravel the thermodynamics, kinetics and reversibility of amphibole oxidation/dehydrogenation reactions. Goals (1) and (2) will be achieved through steady-state and dynamic (isobaric cooling and isothermal decompression) crystallization experiments at high P-T conditions. For goal (3), high-T redox experiments will be performed through thermogravimetric analysis of amphibole using reducing and oxidizing gases (e.g. air, H2). The experimental amphiboles and coexisting phases will be analyzed using optical and electron microscopy, electron microprobe and infrared spectroscopy. Some amphiboles will be characterized through Mössbauer microspectrometry.The results of this research will contribute significantly to the refinement of amphibole thermobarometry and development of speedometers, which are crucially needed to constrain the P (depth)-T conditions of amphibole crystallization and the timescales of processes in magma reservoirs of volcanoes worldwide. Finally, the experimental study of the oxidation/dehydrogenation reaction of amphibole is particularly important to obtain speedometers for constraining the ascent timescales of explosive eruptions.