Reactive flow as a mechanism to form monomineralic rocks in layered intrusions

Layered intrusions represent the fossilised remains of mafic to ultramafic magma bodies. They host significant critical metals and are intensively studied as natural laboratories for igneous processes. The eponymous layers occur over length-scales ranging from millimetres to decametres and are typically interpreted to represent cumulates formed during fractional crystallisation of one or more parental magmas. Most natural melts crystallise several mineral phases at the liquidus to form polymineralic cumulates, but many intrusions also host layers dominated by a single mineral such as olivine, orthoypyroxene, plagioclaise or chromite.Numerous conceptual models have been proposed to explain the formation of monomineralic layers. Most suggest that these layers form when there is restricted stability of minerals crystallising at the liquidus coupled with efficient separation of cumulate minerals and melt. During the formation of a cumulate layer, compaction of a crystal ‘mush’ contributes to melt loss once the melt fraction falls below 40 – 60 %. However, there is a lack of microstructural evidence for compaction, especially to the low melt fraction of adcumulates (