A xenolith from the Delegate breccia pipe, New South Wales, contains sapphirine in equilibrium with aluminous clinopyroxene, pyrope and plagioclase (An48). This unusual assemblage probably developed from a clinopyroxene (+ or - spinel + or - plagioclase) cumulate during cooling from >1400 to -1000oC at P approx 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 stoichiometry of natural sapphirines. Comparisons are made with xenoliths at Stockdale and sapphirine granulites from Finero. Sapphirine is clearly stable under upper-mantle conditions in Ca-Al-Mg-rich bulk compositions.-R.A.H.
|Number of pages||6|
|Publication status||Published - 1986|