Multi-elemental assessment of plagioclase-melt equilibria unravels episodes of crystal growth and provides clues on magma evolution

Violent eruptive events in basaltic systems often follow input of hot, undegassed magmas in shallow magmatic reservoirs. Investigating how crystal and glass chemistry record such physicochemical changes in the system is critical to reconstruct the mechanisms driving sudden large scale explosive events in such settings, and may be integrated with crystal stratigraphy to recover the relative and absolute timing of eruption triggers. As such, it is of utmost importance to reconstruct such changes in natural systems through the record provided by crystals and glasses in the eruption products.

The reconstruction of crystal-melt equilibria is crucial for a thermodynamically rigorous assessment of intensive properties of the magmatic system based on mineral compositions. In this respect, experimental constraints on crystal-melt partitioning are quintessential to the modeling of melt compositions and intensive parameters, performed by minimizing the strain energy determined by the substitution of isovalent trace cations in crystal lattice sites. In this contribution we combine numerical modeling with a multi-elemental approach to the study of intracrystalline compositional variations in a statistically representative data set of plagioclase compositions from Stromboli volcano. This approach, applied to a well-studied volcanic system, allows to constrain the chemical evolution of the system, assessing the role of disequilibrium effects and transient melt compositions existing ephemerally during crystal growth and dissolution episodes. Implications of this work extend from the reconstruction of magma dynamics at Stromboli to the definition of best practices to deal with the interdependence inherent in the treatment of intensive thermodynamic properties of magmatic systems.