[P-PS05] Lunar science and exploration

[PPS05-P06] Viscosity of lunar lavas

*Ryuji Watanabe¹, Akio Goto², Akio Suzuki¹ (1.Department of Earth Science, Graduate School of Science, Tohoku Universuty, 2.Center for Northeast Asian Studies, Tohoku University)

Keywords:viscosity, rotational viscometer, titanium, composition dependence

Viscosity is a parameter related to magma flow and mechanism of eruption, which is considered to be affected by SiO_² and TiO₂. Lunar basalt contains more titanium and iron than Earth's volcanic rock. This is because ilmenite-rich layer was also melted together when basaltic layer beneath the crust re-melted (Shearer and Papike, 1999). Therefore, the viscosity of lunar basaltic magma is thought to be greatly influenced by TiO₂.
In this study, we measured the viscosity of three lunar volcanic glasses, Apollo 14 black glass, Apollo 15 green glass-C, and Apollo 17 orange glass (74220), and discussed the effect of composition on viscosity. Viscosity measurements were performed using a rotational viscometer in the range of 1500℃ to 1270℃ in argon.
It has been found that the viscosity of the magma decreases with increasing TiO₂ content (Zhang and Jahanshahi, 2004). However the lowest viscosity in this measurement was not Apollo 14 black glass with the highest TiO₂ content (16.4 wt%), but Apollo 17 orange glass with an intermediate TiO₂ content (9.12 wt%). TiO₂ works to reduce viscosity, but if its content exceeds a certain amount (perhaps about 10 wt%), its ability to reduce viscosity decreases, and other compositions may be more effective at reducing viscosity.