Rapid crystallization of the Animikie Red Ace Pegmatite,Florence county,northeastern Wisconsin: inclusion microthermometry and conductive-cooling modeling |
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Authors: | Mona-Liza C. Sirbescu Emily E. Hartwick James J. Student |
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Affiliation: | (1) Geology Department, Central Michigan University, 314 Brooks Hall, Mount Pleasant, MI 48859, USA;(2) Present address: Wolverine Gas and Oil Corporation, 1 Riverfront Plaza, 55 Campau NW, Grand Rapids, MI 49503, USA |
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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. |
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Keywords: | Fluid inclusion assemblages Melt inclusion assemblages Microthermometry LCT pegmatite Numerical simulation Undercooling Disequilibrium crystallization Florence county pegmatite field Wisconsin |
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