We evaluated the crystallization regime of a zoned pegmatite dike and the degree of magma undercooling at the onset of crystallization by analyzing coeval fluid and melt inclusion assemblages. The liquidus temperature of the pegmatite magma was ∼720°C, based on re-melting of crystallized-melt inclusions in heating experiments. The magma crystallized sequentially starting with a thin border zone, which formed in less than one day at an average temperature of ∼480°C based on primary fluid inclusions, meaning 240°C undercooling. The primary inclusions from the outer zones were postdated by secondary inclusions trapped between 580 and 720°C, representing fluid exsolved from hotter, still crystallizing inner pegmatite units. The huge temperature contrast between the pegmatite's inner and outer zones was simulated by conductive-heat numerical modeling. A 2.5 m wide dike emplaced in 220°C rocks cools entirely to <400°C in less than 50 days. Unidirectional and skeletal textures also indicate rapid, disequilibrium crystallization.
- Disequilibrium crystallization
- Florence county pegmatite field
- Fluid inclusion assemblages
- LCT pegmatite
- Melt inclusion assemblages
- Numerical simulation