Quantification of nucleation delay in magmatic systems: experimental and theoretical approach

Abstract

We developed a model to predict nucleation delay of olivine, plagioclase, and clinopyroxene in basaltic melts, and alkali feldspar and quartz in felsic melts. The model, based upon classical nucleation theory, was improved by applying modifications inspired by diffuse interface theory. The theoretical calculations were compared to results available in the literature (basalts) and from new experiments on a hydrous (~ 4 wt% water), metaluminous granitic composition conducted in piston cylinder apparatus at 600 MPa and temperatures from 500 to 800 °C. The experimental results and the modelled nucleation delays in silicate melts agree within a factor of ~ 5, which creates an opportunity for better understanding of the nucleation kinetics and crystallization timing of melts of various compositions. We demonstrate the implications of nucleation delay and discuss possible applications of this newly developed model to dry and hydrous felsic melts. We present the nucleation delay of feldspar and quartz in dry rhyolitic melt and its influence on the formation of obsidian, and we compare the nucleation delay of these minerals in a hydrous granitic melt against the typical internal structure of a granitic pegmatite dike.