Experimental constraints of metamorphic pressure and temperature, and phase relations of a phlogopite-bearing orthopyroxene granulite from Howard hills, Napier complex, East Antarctica

Abstract

High-pressure and high-temperature experiments were carried out at 9-13 kbar and 950-1200°C using a piston-cylinder apparatus, simulating the equilibrium conditions of a phlogopite-bearing orthopyroxene granulite from the Howard Hills, Napier Complex, East Antarctica. This granulite consists of orthopyroxene, sapphirine, spinel, alkali feldspar and F-rich phlogopite with minor amounts of plagioclase, rutile and quartz, and is garnet-free. The experiments clarified the equilibrium phase relations of the phlogopite-bearing orthopyroxene granulite under ultrahigh-temperature metamorphism conditions. The following mineral assemblages were obtained with decreasing temperature: orthopyroxene + spinel + liquid, orthopyroxene + phlogopite + spinel + liquid, orthopyroxene + phlogopite + sapphirine + spinel + rutile + liquid, orthopyroxene + alkali feldspar + phlogopite + sapphirine + spinel + rutile, orthopyroxene + alkali feldspar + plagioclase + phlogopite + sapphirine + spinel + rutile. Liquid was found in run products at 9 kbar and temperatures of ≥1100°C, and at pressures of 11-13 kbar and 1150°C. At higher pressure, garnet coexists with orthopyroxene, alkali feldspar, plagioclase, phlogopite, sapphirine, rutile and spinel. These experimental results constrain the P-T conditions of garnet-free, phlogopite-bearing orthopyroxene granulite from the Howard Hills.