An occurrence of sapphirine in the Archean Superior Province, northern Quebec

A clast containing sapphirine has been found in the Troie Complex in the Archean Minto Subprovince, in the northeastern part of the Superior Province, in northern Quebec. The area is dominated by synmagmatically deformed felsic plutonic rocks that host volcano-sedimentary slivers and rafts. The Douglas Harbour Domain contains the Faribault-Thury tonalite-trondhjemite complex, intruded by the 2740-2726 Ma enderbitic Troie Complex. Slivers and enclaves of volcano-sedimentary rocks in the Troie Complex are metamorphosed to granulite grade. A breccia in the core of the Troie Complex contains a heterogeneous population of xenoliths in an enderbitic matrix. The clast contains sapphirine as symplectitic rims with plagioclase or K-feldspar (or with both) developed around sillimanite and cordierite. Sapphirine also forms a corona around green hercynite, with K-feldspar rimming the sapphirine. Reaction textures, annealing and polygonization indicate localized equilibration, with mosaic equilibrium preserved on the thin-section scale. Various geothermobarometers yield estimates of high temperatures (755-1260 degrees C) and pressures (7.5-14 kbar). The existence of localized equilibria is difficult to interpret in terms of simple prograde or retrograde metamorphism linked with orogenesis. Either static P-T conditions for a protracted period, or minimal attainment of granulite-facies conditions are required to produce and preserve these mosaic textures.