Experimental calibration of sapphirine–spinel Fe 2+–Mg exchange thermometer: Implication for constraints on P– T condition of Howard Hills, Napier Complex, East Antarctica

Abstract

The Fe 2+–Mg distribution coefficients between sapphirine and spinel: K D = X Fe Spl X Mg Spr X Mg Spl X Fe Spr , were experimentally determined at pressures of 9–13 kbar and temperatures of 950–1150 °C using a natural ultrahigh-temperature (UHT) granulite with paragenesis of these minerals from the Napier Complex in East Antarctica [ X Mg = Mg / (Fe + Mg); X Fe = Fe / (Fe + Mg)]. A new sapphirine–spinel geothermometer has been obtained as: ln K D = − 1.257 + [ 2940 + 9.5 ( P kbar − 11 ) ] / T (K) . We applied the exchange thermometer to UHT or high-grade metamorphic rocks that were reported from various complexes in the world. If the K D values of 2.63–4.34 obtained from low-Cr mineral pairs such as X Cr Spr < 0.016 and X Cr Spl < 0.047 were substituted into the equation, their temperature conditions would be estimated as 806–1050 °C at 11 kbar. The X Cr means Cr / (Al + Cr(+ Fe 3+)). These temperatures are reasonable retrograde or near peak metamorphic condition.