Occurrence and significance of magmatic inclusions and silicate liquid immiscibility

Abstract

This paper reviews work on magmatic (particularly silicate-melt) inclusions in terrestrial and exetraterrestrial samples and evaluates its significance.
Particular attention is given to silicate liquid immiscibility, as it is frequently a cause for both the trapping of inclusions, and for confusion in their interpretation.
This includes a discussion of immiscibility in the synthetic system K₂O-FeO-Al₂O-SiO₂, and in Iunar and terrestial basalts. For ordinary inclusions, formed during normal magmatic differentiation by crystal fractionation, this review details the trapping mechanisms, the three main changes that may occur within inclusions after they have been trapped (separation of an immiscible fluid phase, crystallization, and leakage), and the five main types of useful data available from such inclusions (temperature of trapping, temperatures and sequence of phase changes during cooling, constraints on maximum minimum cooling rates, bulk composition and the liquid line of descent and the volatile content). Other inclusions in magmatic rocks are trapped and have their composition determined by a variety of types of fluid immiscibility.