Rapid crystallization of the Animikie Red Ace Pegmatite, Florence county, northeastern Wisconsin: Inclusion microthermometry and conductive-cooling modeling

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Abstract

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.

Original languageEnglish
Pages (from-to)289-305
Number of pages17
JournalContributions to Mineralogy and Petrology
Volume156
Issue number3
DOIs
StatePublished - Sep 2008

Keywords

  • Disequilibrium crystallization
  • Florence county pegmatite field
  • Fluid inclusion assemblages
  • LCT pegmatite
  • Melt inclusion assemblages
  • Microthermometry
  • Numerical simulation
  • Undercooling
  • Wisconsin

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