Figure 1

(a) Experimental P and T for APR16 (this study) and MORB⁸ experiments. The green line indicates the liquidus T obtained experimentally¹⁹ for APR16 using MELTS software⁸³ and extrapolated to higher P (dotted segment). (b) and (c) Diagrams showing the logarithm of the measured viscosity on APR16 (this study) plotted as a function of (b) pressure (P) and (c) temperature (T) and compared with the experimental data available for peridotite⁷, MOR basalt⁸, diopside-jadeite (trachy-andesite⁹), albite¹⁰, and dacite¹¹ compositions. The black arrow indicates the pressure at which a viscosity turnover was observed by Sakamaki et al.⁸ for MORBs and explained with the rapid densification (i.e. pressure-induced structural change). The empty circles (b,c) are the viscosities calculated for MORB and APR16 by using the model of Giordano et al.⁵ at ambient P and T of 1200 °C (b) and (c) at the same T of the experiments. Error bars for the viscosity data from this study are within the symbols size. The pressure and temperature uncertainties for our data are ± 0.2 GPa and ~ 50 °C⁷¹, respectively.