TY - JOUR

T1 - Effects of CO2 flushing on crystal textures and compositions

T2 - experimental evidence from recent K-trachybasalts erupted at Mt. Etna

AU - Giuffrida, Marisa

AU - Holtz, Francois

AU - Vetere, Francesco

AU - Viccaro, Marco

N1 - Funding Information: Acknowledgements MG acknowledges the PhD fellowship and two PhD research grants from the University of Catania. This work was also supported by a FIR 2014 project from UniCt to MV (Grant number 2F119B). F. Vetere wishes to acknowledge the European Research Council (ERC) Consolidator Grant ERC-2013-CoG No. 612776— CHRONOS and Marie Curie Fellowship IEF SolVoM#297880 to Diego Perugini. Publisher Copyright: © 2017, Springer-Verlag GmbH Germany. Copyright: Copyright 2017 Elsevier B.V., All rights reserved.

PY - 2017/10/25

Y1 - 2017/10/25

N2 - Changes in magmatic assemblages and crystal stability as a response of CO2-flushing in basaltic systems have rarely been 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 µm and melt pools. This material is representative of an initial magmatic assemblage composed of plagioclase, clinopyroxene and a water-undersaturated melt with 1.6 wt% H2O. In a second step, the initial assemblage was equilibrated at 300 and 100 MPa with fluids having different XCO2 fl (CO2/(H2O + CO2)). At low XCO2 fl (< 0.2 to 0.4), plagioclase is completely dissolved and clinopyroxene show dissolution textures. For relatively high XCO2 fl (0.9 at 300 MPa), the flushing of a CO2-rich fluid phase leads to an increase of the amount of clinopyroxene and a decrease of the abundance of plagioclase at 300 MPa. This decrease of plagioclase proportion is associated with a change in An content. Our experiments demonstrate that flushing basaltic systems with fluids may drastically affect crystal textures and phase equilibria depending on proportions 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 Earth’s 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.

AB - Changes in magmatic assemblages and crystal stability as a response of CO2-flushing in basaltic systems have rarely been 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 µm and melt pools. This material is representative of an initial magmatic assemblage composed of plagioclase, clinopyroxene and a water-undersaturated melt with 1.6 wt% H2O. In a second step, the initial assemblage was equilibrated at 300 and 100 MPa with fluids having different XCO2 fl (CO2/(H2O + CO2)). At low XCO2 fl (< 0.2 to 0.4), plagioclase is completely dissolved and clinopyroxene show dissolution textures. For relatively high XCO2 fl (0.9 at 300 MPa), the flushing of a CO2-rich fluid phase leads to an increase of the amount of clinopyroxene and a decrease of the abundance of plagioclase at 300 MPa. This decrease of plagioclase proportion is associated with a change in An content. Our experiments demonstrate that flushing basaltic systems with fluids may drastically affect crystal textures and phase equilibria depending on proportions 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 Earth’s 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.

KW - Clinopyroxene

KW - CO flushing

KW - Crystal textures

KW - Crystallization experiments

KW - Etna

KW - Plagioclase

UR - http://www.scopus.com/inward/record.url?scp=85032394680&partnerID=8YFLogxK

U2 - 10.1007/s00410-017-1408-3

DO - 10.1007/s00410-017-1408-3

M3 - Article

AN - SCOPUS:85032394680

VL - 172

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 11-12

M1 - 90

ER -