The effect of diffusive re-equilibration time on trace element partitioning between alkali feldspar and trachytic melts

TL;DR

This study investigates how diffusive re-equilibration time affects trace element partitioning between alkali feldspar and trachytic melts through experimental data, revealing the roles of growth rate, composition, and disequilibrium conditions.

Contribution

It provides new experimental insights into the influence of disequilibrium crystal growth and re-equilibration on trace element partitioning in alkali feldspar.

Findings

Ba and Sr behave compatibly and are affected by re-equilibration time.

HFSE and REE are strongly incompatible, with alkali feldspar fractionating LREE from HREE.

Rapid crystal growth promotes disordered growth and reduces partitioning selectivity.

Abstract

We present new experimental data on major and trace element partition coefficients between alkali feldspar and trachytic melt. Experiments were conducted at 500 MPa, 870 890 {\deg}C to investigate through short disequilibrium and long near equilibrium experiments the influence of diffusive re-equilibration on trace element partitioning during crystallization. Our data show that Ba and Sr behave compatibly, and their partition coefficients are influenced by re-equilibration time, orthoclase (Or) content, growth rate and cation order-disorder. High field strength elements (HFSE) and rare earth elements (except Eu) are strongly incompatible, but alkali feldspar efficiently fractionates light (LREE) from heavy rare earth elements (HREE). Our crystallization experiments reveal a strong influence of disequilibrium crystal growth on the partitioning of Ba and Sr. In particular, short-duration experiments show that rapid alkali feldspar crystal growth after nucleation, promotes disordered growth and less selectivity in the partitioning of compatible trace elements that easily enter the crystal lattice (e.g., Ba and Sr)....