  Changes in magmatic assemblages and crystal stability as a response of CO2
flushing in basaltic systems have been never directly addressed experimentally,
making the role of CO2 in magma dynamics still controversial and object of
scientific debate. We conducted a series of experiments to understand the
response of magmas from Etna volcano to CO2 flushing. We performed a first
experiment at 300 MPa to synthesize a starting material composed of crystals of
some hundreds of m and melt pools. This material is representative of an
initial magmatic assemblage composed of plagioclase, clinopyroxene and a water
undersaturated melt. In a second step, the initial assemblage was equilibrated
at 300 and 100 MPa with fluids having different XCO2fl . Our experiments
demonstrate that flushing basaltic systems with fluids may drastically affect
crystal textures and phase equilibria depending on the amount of H2O and CO2 in
the fluid phase. Since texture and crystal proportions are among the most
important parameters governing the rheology of magmas, fluid flushing will also
influence magma ascent to the Earths surface. The experimental results open new
perspectives to decipher the textural and compositional record of minerals
observed in volcanic rocks from Mt. Etna, and at the same time offer the basis
for interpreting the information preserved in minerals from other basaltic
volcanoes erupting magmas enriched in CO2.

Geophysics