Contributions to Mineralogy and Petrology

, Volume 166, Issue 4, pp 959–974

Strontium isotope disequilibrium of plagioclase in the Upper Critical Zone of the Bushveld Complex: evidence for mixing of crystal slurries

  • Sheng-Hong Yang
  • Wolfgang D. Maier
  • Yann Lahaye
  • Hugh O’Brien
Original Paper

Abstract

We report in situ Sr isotope data for plagioclase of the Bushveld Complex. We found disequilibrium Sr isotopic compositions on several scales, (1) between cores and rims of plagioclase grains in the Merensky pyroxenite, the Bastard anorthosite, and the UG1 unit and its noritic footwall, (2) between cores of different plagioclase grains within thin sections of anorthosite and pyroxenite of the Merensky unit, the footwall anorthosite of the Merensky reef and the footwall norite of the UG1 chromitite. The data are consistent with a model of co-accumulation of cumulus plagioclase grains that had crystallized from different magmas, followed by late-stage overgrowth of the cumulus grains in a residual liquid derived from a different level of the compacting cumulate pile. We propose that the rocks formed through slumping of semi-consolidated crystal slurries at the top of the Critical Zone during subsidence of the center of the intrusion. Slumping led to sorting of crystals based on density differences, resulting in a layered interval of pyroxenites, norites and anorthosites.

Keywords

Bushveld Complex Upper Critical Zone Plagioclase In situ strontium isotopes LA-MC-ICP-MS 

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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Sheng-Hong Yang
    • 1
  • Wolfgang D. Maier
    • 1
  • Yann Lahaye
    • 2
  • Hugh O’Brien
    • 2
  1. 1.Department of GeosciencesUniversity of OuluOuluFinland
  2. 2.Geological Survey of FinlandEspooFinland

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