Investigating the structure of silicate melts representative of natural magmas improves our understanding about the rheology of ascending magmas and their behavior once erupted on the surface. In this project, I propose to investigate the effect of pressure on the internal network structure of an alkaline basalt from the Campi Flegrei Volcanic District by using the multi-angle energy dispersive synchrotron X-ray diffraction (EDXD) technique combined with micro-Raman spectroscopy. By the combination of both techniques, I aim to obtain unique and novel information on the arrangement of atoms forming the amorphous structure typical of natural magmas that, in turn, has dramatic effects on the viscosity and explosivity of volcanic eruptions. To achieve the goals of this project, I will reproduce pressure and temperature conditions at which natural magmas might form and undergo before being emplaced at crustal levels within magma chambers. Experimental simulations will be performed using natural lavas like APR16, a K-basalt lithic lava fragment found in the deposits of the Solchiaro tuff in Procida island (Campi Flegrei Volcanic District, south Italy). The application of both in situ X-ray diffraction methods on the synthetic magma at high pressure and temperature followed by spectroscopic Raman techniques at ambient conditions will allow me to model the structure of a melt at the atomic level during decompression and cooling. I expect to obtain important data such as interatomic distances and degree of polymerization that can be used to model the volcanic style of active and quiescent volcanoes knowing the present-day eruptive style and the chemical composition of natural erupted lithic products.
This project aims to study the influence of pressure on the internal structure of an alkaline basalts of the Campi Flegrei Volcanic District. It results to be very innovative from different points of view. First of all, it involves the use of a pioneering technique, the multi-angle energy dispersive X-ray diffraction (EDXD), that has been developed as in situ measurements for liquid silicates on multi anvil and Paris Edinburgh apparatus. To date, this technique has been applied only on synthetic composition that are formed by a limited number of elements; instead, in this project a natural glassy material will be used. In February during the beamtime allocated for Run 2018-1 at the Argonne National Lab I had the possibility to test the EDXD technique on a natural glassy starting material, obtaining results that are very similar to those obtained for synthetic compositions (Bonechi et al., 2018). Thus, this project will provide the first data relative to melt structure measurements performed with EDXD at high pressure on a natural (non-synthetic) composition representative of the Italian volcanism. Another relevant and innovative aspect is linked to the Campi Flegrei Volcanic District, to which the investigated sample belongs. Indeed, there are not work of any kind that investigate the melt structure at high and/or atmospheric pressure. So, the results related to this project would provide unique information about the structure of this alkaline melt from high to atmospheric pressure with relevant implications on the actual knowledge of the magmatic system since it is closely related to other parameters as viscosity, compressibility, conductivity, density, molar volume, liquidus phase relations and other thermodynamic properties. Especially, in this area that is one of the most dangerous volcanic system in the world.
Bonechi et al. 2018. EMPG XVI-Abstracts Volume, p. 10, 16th International Conference on ¿Experimental Mineralogy, Petrology and Geochemistry¿, Clermont Ferrand, France