Density of high-Ti basalt magma at high pressure and origin of heterogeneities in the lunar mantle

The density of the Apollo 14 black glass melt, which has the highest TiO2 content of pristine mare glasses, was measured to 4.8 GPa and 2100 K using an X-ray absorption method. A fit of the pressure–density–temperature data to the high-temperature Birch–Murnaghan equation of state yielded the isothermal bulk modulus KT0 = 9.0 ± 1.2 GPa, its pressure derivative K0′ = 16.0 ± 3.4, and the temperature derivative of the bulk modulus (∂KT/∂T)P = −0.0030 ± 0.0008 GPa/K at 1700 K. The high-Ti basalt magma is less dense than the lunar mantle below about 1.0 GPa. Therefore, the high-Ti basalt magma produced in the hybridized source (100–200 km) can ascend to the lunar surface. The basalt formed at the higher pressure could not ascend but move downwards, and solidify in the lunar mantle. The solidified high-Ti basalt components can create chemical heterogeneities in the lunar mantle and can cause the low-velocity anomalies observed seismologically.