Heterogeneous Reactions - The Gibbs Method

Silicate melt - mineral equilibria MELTS - latest update Ghiorso and Sack (1995) Contrib. Mineral. Petrol. 119: 197-212. Multiply-saturated liquids Grove et al. (1992) Amer. Geophys U Mono. 71: 281-310. Langmuir et al. (1992) Amer. Geophys U Mono. 71: 183-280. Ariskin et al. (1993) Сотр. Geosci 19: 1155 -1170. Yang et al. (1996) Contrib. Mineral. Petrol. 124: 1 -18. Plagioclase - liquid Panjasawatwong et al. (1995) Contrib. Mineral. Petrol. 118: 420-432. Housh and Luhr (1991) Amer. Mineral. 76: 477 -492. 3 Some thermodynamic models for silicate mineral/melt equilibria Direct approach using solution calorimetry Weill, Hon and Navrotsky in Hargraves, ed. "Physics of magmatic processes" р.49-89. Other empirical models Langmuir and Hanson (1981) In Newton et al., eds. "Thermo of minerals and melts Glazner (1984) Contrib Mineral Petrol 88:260-268. Burnham and Nekvasil (1986) Amer. Mineral. 71:239-263. Nielsen and Dungan (1983) Contrib Mineral Petrol 84:310-326. Russel and Nichols (1985) Canad. Mineral. 23:479-488. Nielsen (1988) Geochim. Cosmochim. Acta 52:27-39. Weaver and Langmuir (1990) Computers and Geosciences 16:119. Overviews/Reviews Reviews in Mineralogy, v. 17, Thermodynamic modeling of geological materials: Minerals, fluids and melts (1987) Reviews in Mineralogy, v. 24, Modern methods of igneous petrology: Understanding magmatic processes (1990) Silicate mineral - silicate melt equilibria and models Olivine - Liquid Roeder and Emslie (1970) Contrib Mineral. Petrol. 29, 275-289. А highly successful empirical model that uses mineral/melt partition coefficients(�'s). R&E found а strong temperature dependence for the formation rea�ns of th�orsterite and fayalite olivine components from liquid cofg�nts (� g and Кр е), and а nearly temperature independent exchange KD - 8. Longhi et al. (1978) Geochim CosmochimActa 42, 1545-1558. Longhi uses а Temkin -like model for silicate melts, and adds an empirical correction factor. Si/O, Si/(Si+Al) and several other mixing models are assumed. This data set spans а wide range in composition space, and shows that there are activity effects in both the network rnodifier and network former "sites" in siJicate melt. Herzberg (1979) Geochim. Cosmochim. Acta ,43, 1241-1251. Herzberg attempts to evaluate the activity coefficient for Mg2 + + and Sio4- in silicate Ьу looking at the formation reaction of forsterite from these two melt components. Herzberg assumes ideal mixing in the Mg-Fe system, and then adds CaAI and alkali� as components. Не formulates acti�ty coefficie�s for th�se al�a y components wh1ch account for the effects of the alkal1s on the Mg + spec1es. S1O activity is not specifically dea]t with in the model. Ford et al. (1983) J. Petrol. 24, 256-265. А completely empirical model which fits 11 olivine/liquid partition coefficients in terms of compositional parameters. Silica activity is not considered in the model, �xcept as а· fit coefficient. The other fit coefficients are the sum of network formers (Mg, Fe, Са, Mn, Cr, and Ni), Al, Na+K, etc., Т and Р. 11 Nielsen and Dungan (1983) Contrib Mineral. Petrol. 84, 310-326. The mixing properties of silicate melts are modeled assuming that the melt components mix оп two sites. Опе is composed of network former components (Si, КАI, NaAI, CaAI, MgAI, FeAl) and the other of network modifiers (the oxides of Mg, Fe, Са, Na, К). Melt component activities are calculated Ьу assuming ideal mixing оп each of these two melt sites. Therefore, melt activities are simply the normalized mo]e fraction of the species on the site. There is no free energy of mixing assumed between the network former and network modifier site. Glazner et al. (1984)Contrib Mineral. Petrol. 88, 260-268. This paper calculates standard state free energy values for melt and olivine and plagioclase. Component choice in the silicate melt are the mineral components forsterite and fayalite. Activity of Fo and Fa in the melt are calculated as second