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

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Abstract

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. Keywords Fluid inclusion assemblages Melt inclusion assemblages Microthermometry LCT pegmatite Numerical simulation Undercooling Disequilibrium crystallization Florence county pegmatite field Wisconsin
Original languageEnglish
Pages (from-to)289-305
JournalContributions to Mineralogy and Petrology
Volume156
Issue number3
StatePublished - Mar 12 2008

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