Skip to main content
Journal cover image

Discordant bodies from olivine-bearing zones III and IV of the Stillwater Complex, Montana - evidence for postcumulus fluid migration and reaction in layered intrusions

Publication ,  Journal Article
Meurer, WP; Klaber, S; Boudreau, AE
Published in: Contributions to Mineralogy and Petrology
December 1, 1997

Mineralogically zoned and unzoned discordant bodies composed predominantly of plagioclase with up to 35% olivine, occur at three different levels in Olivine-Bearing zones III and IV of the Middle Banded series of the Stillwater complex. The discordant bodies are elongate perpendicular to the layering of the host cumulates with slender concordant apophyses. Although the host olivine-gabbros are foliated with tabular plagioclase, the discordant bodies lack a discernible fabric and have blocky plagioclase. Average olivine in the host rocks is slightly more magnesian than that of the discordant bodies (Mg£75.8 ± 0.7 versus Mg£74.6 ± 0.3 respectively) but plagioclase compositions are indistinguishable (An77.6 ± 2.0 versus An76.6 ± 4.3 - average host and discordant bodies respectively). Whole-rock major- and trace-element compositions of the discordant bodies are generally indistinguishable from cumulates with similar modal abundance. However, bulk compositions of anorthositic cores from the discordant bodies are enriched in K, Na, Ba, Sr and P. We conclude that the discordant bodies formed when cooler volatile fluids or fluid-rich silicate liquids moved upward and encountered a hotter undersaturated solid-plus-liquid assemblage. Continued liquid/fluid fluxing increased the permeability along the flow path and focused the flow, allowing the original bulk compositions to be modified and leaving plagioclase-rich troctolites and anorthosites. The shapes of the discordant bodies suggest that the cumulus pile had anisotropic permeability during late-stage liquid/fluid flow. Chemical and mineralogical evidence from other parts of Olivine-Bearing zones III and IV suggests that the processes that formed the discordant bodies may have influenced other cumulates. In fact, it appears that the same processes that formed the discordant bodies operated within an anorthositic layer, strongly modifying the chemistry of the rock but leaving no mineralogical or textural evidence.

Duke Scholars

Published In

Contributions to Mineralogy and Petrology

DOI

ISSN

0010-7999

Publication Date

December 1, 1997

Volume

130

Issue

1

Start / End Page

81 / 92

Related Subject Headings

  • Energy
  • 4019 Resources engineering and extractive metallurgy
  • 3705 Geology
  • 3703 Geochemistry
  • 0499 Other Earth Sciences
  • 0403 Geology
  • 0402 Geochemistry
 

Citation

APA
Chicago
ICMJE
MLA
NLM
Meurer, W. P., Klaber, S., & Boudreau, A. E. (1997). Discordant bodies from olivine-bearing zones III and IV of the Stillwater Complex, Montana - evidence for postcumulus fluid migration and reaction in layered intrusions. Contributions to Mineralogy and Petrology, 130(1), 81–92. https://doi.org/10.1007/s004100050351
Meurer, W. P., S. Klaber, and A. E. Boudreau. “Discordant bodies from olivine-bearing zones III and IV of the Stillwater Complex, Montana - evidence for postcumulus fluid migration and reaction in layered intrusions.” Contributions to Mineralogy and Petrology 130, no. 1 (December 1, 1997): 81–92. https://doi.org/10.1007/s004100050351.
Meurer, W. P., et al. “Discordant bodies from olivine-bearing zones III and IV of the Stillwater Complex, Montana - evidence for postcumulus fluid migration and reaction in layered intrusions.” Contributions to Mineralogy and Petrology, vol. 130, no. 1, Dec. 1997, pp. 81–92. Scopus, doi:10.1007/s004100050351.
Journal cover image

Published In

Contributions to Mineralogy and Petrology

DOI

ISSN

0010-7999

Publication Date

December 1, 1997

Volume

130

Issue

1

Start / End Page

81 / 92

Related Subject Headings

  • Energy
  • 4019 Resources engineering and extractive metallurgy
  • 3705 Geology
  • 3703 Geochemistry
  • 0499 Other Earth Sciences
  • 0403 Geology
  • 0402 Geochemistry