New Delhi: Scientists from IIT Kharagpur and the Physical Research Laboratory (PRL) have successfully simulated the extreme conditions of the lunar interior to solve a long-standing mystery, one of how the Moon produced its unique titanium-rich volcanic rocks. The study, published in Geochimica et Cosmochimica Acta, utilised high-pressure ‘piston-cylinder’ experiments at IIT Kharagpur to mimic the lunar mantle at depths between 200 and 700 kilometres. By recreating iron-titanium-rich minerals within the magnesium-rich lunar mantle, the team recreated the chemical signatures of intermediate and high-titanium basalts, similar to the samples returned by USA’s Apollo and China’s Chang’e-5 missions.
Scientists believe that as the ancient lunar magma ocean solidified, a dense layer of minerals called ilmenite-bearing cumulates (IBC) formed near the crust. Due to their high density, these minerals eventually sank into the lighter, deeper mantle, a process known as lunar mantle overturn. The researchers demonstrated that as this titanium-rich layer sank and began to melt, it interacted with the surrounding mantle. This interaction is the critical ‘missing link’ in explaining why lunar basalts contain up to 18 per cent titanium dioxide, while the basalts on Earth contain less than two per cent. The experiments suggest a complex journey for lunar magma.
Implications for lunar history
The moderately titanium-rich melts can rise directly to the surface, erupt, and form intermediate-titanium basalts. The more titanium-rich melts are too dense to rise, they sink deeper, crystalize, mix with the ascending low-titanium magmas, with the mixture becoming buoyant enough to rise and erupt, forming the high-titanium basalts seen in the lunar ‘seas’ or maria. The findings confirm that these chemical interactions were physically possible throughout the volcanic history of the Moon. The model slightly underestimated certain levels of aluminium-rich minerals, but the researchers suggest that incorporating small chunks of crustal material can resolve the discrepancy. The work provides a new, viable mechanism to explain the volcanic landscape and its composition observed on the lunar surface today.