Thermal expansion of talc at high temperature and implications for the exhumation of eclogites in subduction zones

Abstract

The thermal expansion coefficient of talc has been measured using a high-temperature thermal optical expansion apparatus over a temperature range of 296 to 1473 K. The results show a gradual increase in the thermal expansion coefficient between 296 and 1086 K, and a rapid and substantial increase between 1086 and 1316 K, but exhibit a decline trend between 1316 and 1473 K. At lower temperatures, changes in crystal structure are the primary mechanism governing thermal expansion; at higher temperatures, the dehydration phase transition and the resulting formation of cracks are the primary contributors to thermal expansion. The volume of talc exhibits a linear increase with temperature, described by the equation:\(V/{V}_{0}=1+2.153 \left( \pm 0.011\right)\times {10}^{-5} \left(T-296\right)\). At high temperatures (573–1073 K), by fitting the expansion data to the Grüneisen thermal equation of state, bulk modulus K_0​ = 47.3 ± 0.9 GPa, pressure derivative \({K}_{0}^{{\prime }}\left(T\right)\) = 6.2 ± 0.4, cell volume V₀​ = 904.5 ± 0.6 ų, and Debye temperature θ = 829.3 ± 0.6 K were obtained at 0 K. The presence of talc reduces the density of subduction zones, facilitating the exhumation of oceanic eclogites.