Knowledge of density and compressibility of volatile-bearing silicate melts under relevant pressure and temperature conditions is essential for understanding the dynamics of magmatic systems in the lower crusts and upper mantle. For example, the density contrast between the melt and the surrounding rocks provides the driving force for the rising of the melts within the crust, controls the stratification of igneous bodies, melt segregation as well as fractionation and partial melting processes. However, the determination of these properties at simultaneous high-pressure, high-temperature conditions is not straightforward and data is available only for a very limited range of pressures, temperatures and compositions. This proposal aims at determining the density of dry and hydrous silicate melts at pressure and temperature conditions relevant for subduction zone and crustal settings.
In the first part of the project, the density and structure of water-bearing andesitic and basaltic liquids (5 to 10 wt% H2O) will be determined by X-ray absorption and X-ray diffraction at conditions that pertains to magmatic processes (up to 4 GPa and 2100 K) using a Paris-Edinburgh press and synchrotron radiation. These experiments will result in the first experimentally derived equation of state of andesitic and basaltic liquids and builds up on recent work conducted in our group to determine the density of hydrous granitic (with support from SNF200021_13011234) and water and CO2-bearing alkaline magmas. On the other hand, the density of water-rich granite-H2O liquids (> 25 wt% H2O) will be determined up to 1200 K and 3 GPa from acoustic velocity measurements in an externally heated diamond anvil cell using Brilouin scattering spectroscopy. Both approaches are complementary and necessary to determine the density of hydrous silicate melts on broad range of pressure, temperature and compositions of geological relevance.
Density and structural data obtained in this project will be combined with literature data on hydrous peridotite liquids and own results for granites and alkaline magmas to implement a general model to predict the density of hydrous magmatic liquids down to the top of the upper mantle. Such a model will be of fundamental importance to address some of the most important open questions in igneous petrology, including magma differentiation, melt migration and emplacement in the crust, which will lead to a better understanding of crust formation processes.