ELSEWIER Earth and Planetary Science Letters 153 (1997) 209-222 EPSL Melting enthalpies of mantle peridotite: calorimetric determinations in the system CaO-MgO-Al,O,-SiO, and application to magma generation Hiroshi Kojitani ‘, Masaki Akaogi * zyxwvutsrqponmlkjihgfedcbaZYXW Department of Chemistry, Faculp of Science, Gakushuin UniLlersim.1-5-l Mejiro, Toshima-ku. Tokyo 171. Japan Received 27 March 1997; accepted 29 September 1997 zyxwvutsrqponmlkjihgfedcbaZYXWVUTS Abstract High-temperature drop calorimetry in the temperature range of 139% 1785 K was performed for the samples of mixtures of synthetic anorthite (An), diopside (Di), enstatite (En) and forsterite (Fo) with the same compositions as those of primary melts generated at 1.1, 3 and 4 GPa at most 10” above the solidus of anhydrous mantle peridotite in the CaO-MgO-Al,O,- SiO, system. From the differences between the heat contents zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH (H, - Hzg8) of liquid and that of crystal mixture at the liquidus temperature, melting enthalpies of the samples of 1.1, 3 and 4 GPa-primary melt compositions were determined at 1 atm to be 531 + 39 J. g-’ at 1583 K, 604 & 21 J. g-’ at 1703 K, 646 + 21 J. g-’ at 1753 K, respectively. These heat of fusion values suggest that mixing enthalpy of the melt in the An-Di-En-Fo system is approximately zero within the experimental errors when we use the heat of fusion of Fo by Richet et al. (P. Richet, F. Leclerc, L. Benoist, Melting of forsterite and spinel, with implications for the glass transition of MgzSiO, liquid, Geophys. Res. Lett. 20 (1993) 1675- 1678). The measured enthalpies of melting at 1 atm were converted into those for melting reactions which occur under high pressures by correcting enthalpy changes associated with solid-state mineral reactions. Correcting the effects of pressure, temperature and Fe0 and Na,O components on the melting enthalpies at 1 atm, heat of fusion values of a representative mantle peridotite just above the solidus under high pressure were estimated to be 590 J at 1.1 GPa and 1523 K, 692 J at 3 GPa and 1773 K, and 807 J at 4 GPa and 1923 K for melting reactions producing liquid of 1 g, with uncertainties of 50 J. By applying these melting enthalpies to a mantle diapir model which generates present MORBs, a potential mantle temperature of 1533 K has been estimated, assuming an eruption temperature of magma of 1473 K. 0 1997 Elsevier Science B.V. Keywords: melting; enthalpy; mantle ; peridotite; high-temperature ; calorimetry; melts; mantle plumes 1. Introduction * Corresponding author. Fax: + 81 3 5992.1029; E-mail: masaki.akaogi@gakushuin.ac.jp ’ Earth Science Laboratory, Graduate School of Social and Cultural Studies, Kyushu University, 4-2-l Ropponmatsu, Chuo- ku, Fukuoka 810, Japan. Fax: +81 3 5992-1029. Physical models of magma generation in the earth’s mantle have been extensively developed for the last decade [l-4]. These models require heat of 0012-821X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII SOOl2-821X(97)00186-6