Mantle-Derived Sapphirine

W. L. Griffin and S. Y. O'Reilly
Mineralogisk-Geologisk Museum, Sars Gate 1, 0562, Oslo 5, Norway
School of Earth Sciences, Macquarie University, North Ryde, NSW 2113, Australia

Abstract: A xenolith from the Delegate breccia pipe (New South Wales, Australia) contains sapphirine in equilibrium with aluminous clinopyroxene, garnet, and plagioclase (An48). This unusual assemblage probably developed from a clinopyroxene (±spinel ± plagioclase) cumulate during cooling from > 1400°C to c. 1000°C at pressures near 15 kbar. The sapphirine is close to the 7:9:3 composition, suggesting that bulk composition is more important than P-T conditions in determining the stoichiometry of natural sapphirines. A similar occurrence of sapphirine has also been recorded in mantlederived xenoliths from the Stockdale kimberlite in Kansas. Re-examination of sapphirine granulites from Finero suggests that their primary assemblages and origin may have been similar to those of the Delegate xenolith. Sapphirine is clearly stable under upper-mantle conditions in Ca-Al-Mg-rich bulk compositions.

Mineralogical Magazine; December 1986 v. 50; no. 358; p. 635-640; DOI: 10.1180/minmag.1986.050.358.08
© 1986, The Mineralogical Society
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