Temperature-dependent thermal expansivities of multicomponent natural melts between 993 and 1803 K

Abstract

The thermal expansivities of three multicomponent glasses and liquids have been obtained over a large temperature interval (298 – 1803 K) which combine the results of low and high temperature measurements. The sample compositions investigated were derived from three natural lavas; Vesuvius 1631 eruption, Etna 1992 eruption and an Oligocene–Miocene lava flow from Slapany in the Bohemian massif. The original rocks are tephriphonolite, trachybasalt and basanite, respectively. The density values of the glassy samples were derived from dilatometic measurements of each sample after cooling at 5 K min − 1 at 298 K, followed by measurements of the glass thermal expansion coefficient from 298 K to the samples' respective glass transition interval. Supercooled liquid volumes and thermal molar expansivities were determined by combining scanning calorimetric and dilatometric measurements, assuming that the kinetics of enthalpy and shear relaxation are equivalent [Webb, S.L., 1992. Shear, volume, enthalpy and structural relaxation in silicate melts. Chem. Geol. 96, 449–457.]. Thermal molar expansivity at supercooled liquid temperature varies from 16.86 ± 0.48 × 10 − 4 cm 3 mol − 1 K − 1 for basalt/basanite, to 18.99 ± 0.48 × 10 − 4 cm 3 mol − 1 K − 1 for trachybasalt, and 20.98 ± 0.62 × 10 − 4 cm 3 mol − 1 K − 1 for tephriphonolite. High temperature densities were measured using Pt double bob Archimedean densitometry. Across the super-liquidus temperature interval investigated, the densities range from 2.655 ± 0.002 to 2.708 ± 0.012 g cm − 3 for basalt–basanite, from 2.578 ± 0.003 to 2.601 ± 0.002 g cm − 3 for trachybasalt and 2.458 ± 0.006 from 2.467 ± 0.002 g cm − 3 to tephriphonolite. In addition, the oxidation state of iron was analyzed using a wet chemistry method. The measured high temperature densities have been compared with predicted densities across the same temperature interval calculated using the multicomponent density models of Lange and Carmichael [Lange, R.A., Carmichael, I.S.E., 1987. Densities of Na 2O–K 2O–CaO–MgO–FeO–Fe 2O 3–Al 2O 3–TiO 2–SiO 2 liquids: new measurements and derived partial molar properties. Geochim. Cosmochim. Acta 51, 2931–2946.] and Lange [Lange, R.A., 1997. A revised model for the density and thermal expansivity of K 2O–Na 2O–CaO–MgO–Al 2O 3–SiO 2 liquids from 700 to 1900 K: extension to crustal magmatic temperatures. Contrib. Mineral. Petrol. 130, 1–11]. The resulting data for volumes near glass transition temperature (993 – 1010 K) and at super-liquidus temperature (1512 – 1803 K) are combined to yield temperature-dependent thermal expansivities over the entire supercooled and stable liquid range. These results confirm the observation of Knoche et al. [Knoche, R., Dingwell, D.B., Webb, S.L., 1992a. Non-linear temperature dependence of liquid volumes in the system albite–anorthite–diopside. Contrib. Mineral. Petrol. 111, 61–73], Knoche et al. [Knoche, R., Dingwell, D.B., Wegg, S.L., 1992b. Temperature-dependent thermal expansivities of silicate melts: the system anorthite–diopside. Geochim. Cosmochim. Acta 56, 689–699], Toplis and Richet [Toplis, M.J., Richet, P., 2000. Equilibrium density and expansivity of silicate melts in the glass transition range. Contrib. Mineral. Petrol. 139, 672–683], Gottsmann and Dingwell [Gottsmann, J., Dingwell, D.B., 2002. Thermal expansivities of supercooled haplobasaltic liquids. Geochim. Cosmochim. Acta 66 (12) 2231–2238] of the temperature dependence of thermal expansivity. In the systems investigated here, the temperature dependence of thermal expansivity increases from basalt/basanite to tephriphonolite compositions.