Experimental calibration of the sphalerite cosmobarometer

The pressure and temperature dependence of the composition of sphalerite in equilibrium with troilite + metallic iron has been determined experimentally at 2.5 and 5.0 kbar between 400° and 800°C using both the aqueous and anhydrous alkali halide flux recrystallization techniques. The measured pressure effect is larger than that calculated by us and by Schwarczet al. (1975a), and is described by the equation (T in Kelvins), P (kbar) = ?3.576 + 0.0551T ?0.0296Tlogmole % FeS.Assuming temperatures of final equilibration between sphalerite and troilite of 350°C for iron meteorites and 600°C for enstatite chondrites, published analyses of sphalerites provide estimates of pressures of formation and possible radii of parent objects of meteorites as follows: IA irons (Landes, Sardis, Gladstone, Bogou, Odessa, Toluca) 0.0 to 3.5 kbar, 0 to 442 km; E6 enstatite chondrites (Yilmia, Pillistfer) ?0.2 to 0.7 kbar, 0 to 198 km.