Evolution of magmatic and subsolidus AFM mineral assemblages in granitoid rocks: Biotite, muscovite, and garnet in the Cuffytown Creek pluton, South Carolina

Journal Article · · American Mineralogist; (United States)

OSTI ID:6917778

Speer, J A ^[1]; Becker, S W

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1. North Carolina State Univ., Raleigh (United States)

The Cuffytown Creek pluton is a leucocratic alkali feldspar granite with (F + Mn)-rich biotite, muscovite, garnet, and fluorite as varietal minerals. Bt [plus minus] Ms is preserved as inclusion assemblages in quartz; Bt + Ms [plus minus] Grt and Ms + Grt are matrix assemblages. The inclusion assemblages are interpreted as early magmetic, and the matrix assemblages as late magmatic with superimposed subsolidus partial reequilibration. In sequence, the AFMMn crystallization reactions are liquid = Bt, liquid = Bt + Ms, liquid + Bt = Ms + Grt, and liquid = Grt + Ms. Inclusion biotite shows FeMg[sub [minus]1] and Mn(Fe,Mg)[sub [minus]1] exchanges, which may reflect both change in melt composition and cooling along an f[sub O[sub 2]] buffer. Inclusions of white mica are nearly end-member muscovite. Evolution from inclusion to matrix mica compositions shows narrowing of the compositional gap between the dioctahedral and trioctahedral micas, as well as OHF[sub [minus]1] and MnMg[sub [minus]1] exchanges in the biotite and (Fe[sup 2+], Mg,Mn)Si[sup [6]]Al[sub [minus]1][sup [4]]Al[sub [minus]1] (celadonite), NaK[sub [minus]1], OHF[sub [minus]1], and Ti enrichment in the white micas. Garnets are spessartine-almandine. Subsolidus replacement textures, mineral compositions, and fluid buffers result from two reactions that are estimated to have occurred at 300-400 C: (1) plagioclase + iron biotite + muscovite + iron chlorite + fluid = albite + potassium feldspar + magnesium biotite + phengite + magnesium chlorite + fluorite + quartz and (2) garnet + potassium feldspar + fluid = muscovite + rhodochrosite + quartz.

• DOE Contract Number: AC05-78ET27001
• OSTI ID: 6917778
• Journal Information: American Mineralogist; (United States), Journal Name: American Mineralogist; (United States) Vol. 77:7-8; ISSN AMMIAY; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
BIOTITE
CHEMICAL REACTION KINETICS
CRYSTALLIZATION
DEVELOPED COUNTRIES
FLUORITE
GARNETS
GRANITES
HALIDE MINERALS
IGNEOUS ROCKS
KINETICS
MAGMATISM
MICA
MINERALIZATION
MINERALOGY
MINERALS
MUSCOVITE
NORTH AMERICA
OXYGEN COMPOUNDS
PETROCHEMISTRY
PETROGENESIS
PHASE STUDIES
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
REACTION KINETICS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SOUTH CAROLINA
TEXTURE
USA