Experimental measurements of the viscosity and melt structure of alkali basalts at high pressure and temperature

Barbara Bonechi,Yoshio Kono,Mario Gaeta,Luca Ziberna,Vincenzo Stagno,Cristina Perinelli,Giovanni B Andreozzi,Rostislav Hrubiak

doi:10.1038/s41598-022-06551-7

Abstract

Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscosity- driven processes of melt migration from source rocks at upper mantle depths. In this experimental study, we investigated the effect of pressure (0.7–7.0 GPa) and temperature (1335–2000 °C) on the viscosity and the atomic melt structure of a synthetic anhydrous primitive alkaline basalt, an analogue of the pre-eruptive magma that likely feeds the Campi Flegrei Volcanic District at present day. Obtained viscosities (0.5–3.0 Pa s), mobility (0.1–0.4 g cm3 Pa−1 s−1) and ascent velocity (1.5–6.0 m yr−1) are presented to support geochemical and geophysical observations of Campi Flegrei as a critical volcanic district currently undergoing gradual magma recharge at depth.

Highlights

Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscositydriven processes of melt migration from source rocks at upper mantle depths
We calculated the viscosity for the simplified synthetic mid-ocean ridge (MOR) basalt and APR16 liquid composition by using the model of Giordano et al.[5] (GRD model) at ambient P and 1200 °C ( H2O set to the minimum value of 0.02 wt% allowed by the model constraints)
Despite their similar 1-atm viscosity, this prediction highlights the important effect that P has on the viscosity of basaltic compositions

Summary

Introduction

Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscositydriven processes of melt migration from source rocks at upper mantle depths In this experimental study, we investigated the effect of pressure (0.7–7.0 GPa) and temperature (1335–2000 °C) on the viscosity and the atomic melt structure of a synthetic anhydrous primitive alkaline basalt, an analogue of the pre-eruptive magma that likely feeds the Campi Flegrei Volcanic District at present day. Additional studies have provided empirical numerical models to determine the viscosity of melt compositions spanning terrestrial volcanic rocks from basic to silicic, from subalkaline to peralkaline, and from metaluminous to p eraluminous[5] (and references therein) These viscosity models can be safely used to model the viscosity at atmospheric conditions (e.g., lava emplacement) or for shallow magma bodies or conduits where the effect of pressure can be considered negligible. The obtained results were used to estimate the mobility and ascent rate of anhydrous APR16-like magmas that we propose being representative of the primitive magmas feeding up the actual Campi Flegrei Volcanic District, and to reconstruct the depth at which their source might be located

Methods

Results

Conclusion