Petrogenetic relationships between pegmatite and granite based on geochemistry of muscovite in pegmatite wall zones, Black Hills, South Dakota, USA
- Washington Univ., St. Louis, MO (United States)
- Univ. of New Mexico, Albuquerque (United States)
The compositions of large samples of granitic pegmatite wall zones have been determined for a suite of ten pegmatites of diverse geochemical character and degree of compositional evolution in the Keystone area of the Black Hills. Whole-rock compositions are strongly peraluminous, and they deviate substantially from the granite minimum composition in quartz-albite-orthoclase normalized components, showing considerably more scatter than Harney Peak Granite whole rocks. Wall-zone minerals are commonly coarsely segregated, leading to large modal variability among whole rocks. These features make whole-rock samples of wall zones unsuitable for the determination of initial pegmatite bulk compositions. Trace and minor element compositions of muscovite separates from the wall zones were thus determined to eliminate the effects of modal variability on trace element concentrations so that geochemical differences between pegmatites could be modeled. Estimates of initial pegmatite melt trace element concentrations range from 800-4,000 ppm Rb, 100-1,000 ppm Cs, 200-2,000 ppm Li, and 1-50 ppm Ba. Trace element concentrations of muscovite from a given pegmatite generally cluster together, although several show considerable intra-pegmatite scatter, and there are large overlaps among different pegmatites. The geochemical characteristics of samples from the Etta pegmatite indicate mixing with and assimilation of country rocks. Exceptionally low Rb/Cs ratios of muscovite from the Etta pegmatite and similar to those of muscovite from K-feldspar-rich assemblages of other pegmatites where the Rb concentration of melt may have been buffered by crystallizing assemblages that had bulk Rb distribution coefficients close to 1.
- DOE Contract Number:
- FG01-84ER13259
- OSTI ID:
- 7206245
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 56:5; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GEOLOGIC FORMATIONS
GEOCHEMISTRY
GRANITES
MUSCOVITE
PEGMATITES
SOUTH DAKOTA
ABSORPTION SPECTROSCOPY
ALBITE
BARIUM
CALCIUM
CESIUM
CHEMICAL COMPOSITION
CRYSTALLIZATION
DATA ANALYSIS
ELECTRON MICROPROBE ANALYSIS
EXPERIMENTAL DATA
FLUORINE
GEOLOGIC HISTORY
GEOLOGY
IRON
LITHIUM
MANGANESE
MAPS
MINERALOGY
MINERALS
NIOBIUM
ORTHOCLASE
POTASSIUM
QUARTZ
RUBIDIUM
SAMPLING
STRONTIUM
TANTALUM
TRACE AMOUNTS
VARIATIONS
X-RAY DIFFRACTION
ZINC
ALKALI METAL COMPOUNDS
ALKALI METALS
ALKALINE EARTH METALS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CHEMICAL ANALYSIS
CHEMISTRY
COHERENT SCATTERING
DATA
DEVELOPED COUNTRIES
DIFFRACTION
ELEMENTS
FEDERAL REGION VIII
FELDSPARS
HALOGENS
IGNEOUS ROCKS
INFORMATION
METALS
MICA
MICROANALYSIS
NONDESTRUCTIVE ANALYSIS
NONMETALS
NORTH AMERICA
NUMERICAL DATA
OXIDE MINERALS
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
POTASSIUM COMPOUNDS
POTASSIUM SILICATES
ROCKS
SCATTERING
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SPECTROSCOPY
TRANSITION ELEMENTS
USA
580000* - Geosciences