New research has cracked a vital process in the creation of unique lunar rock types from the Moon.
The discovery explains the signature composition of lunar rocks and their presence on the lunar surface, unravelling a mystery which has long eluded scientists.
A combination of high-temperature laboratory experiments using molten rocks and sophisticated isotopic analyses of lunar samples identify a critical reaction that controls their composition.
The research, ‘Titanium-rich basaltic melts on the Moon modulated by reactive flow processes,’ is published in Nature Geoscience.
The origins of volcanic lunar rocks
This reaction took place in the deep lunar interior some three and a half billion years ago, involving the exchange of the element iron (Fe) in the magma with the element magnesium (Mg) in the surrounding rocks, modifying the chemical and physical properties of the melt.
Tim Elliott, Professor of Earth Sciences at the University of Bristol and co-lead author of the study, said: “The origin of volcanic lunar rocks is a fascinating tale involving an ‘avalanche’ of an unstable, planetary-scale crystal pile created by the cooling of a primordial magma ocean.
“Central to constraining this epic history is the presence of a magma type unique to the Moon, but explaining how such magmas could even have got to the surface, to be sampled by Space missions, has been a troublesome problem.
“It is great to have resolved this dilemma.”
High-Ti basalts are widespread on the Moon
Surprisingly high concentrations of the element titanium (Ti) in parts of lunar rocks have been known since the NASA Apollo missions back in the 1960s and 1970s, which successfully returned solidified, ancient lava samples from the Moon’s crust.
More recent mapping by orbiting satellites shows these magmas, known as ‘high-Ti basalts’, to be widespread on the Moon.
“Until now, models have been unable to recreate magma compositions that match essential chemical and physical characteristics of the high-Ti basalts,” explained Dr Martijn Klaver, Research Fellow at the University of Münster Institute of Mineralogy and co-lead author.
“It has proven particularly hard to explain their low density, which allowed them to be erupted some three and a half billion years ago.”
The international team of scientists, led by the Universities of Bristol in the UK and Münster in Germany managed to mimic the high-Ti basalts in the process in the lab using high-temperature experiments.
Measurements of the high-Ti basalts also revealed a distinctive isotopic composition that provides a fingerprint of the reactions reproduced by the experiments.
Both results clearly demonstrate how the melt-solid reaction is integral in understanding the formation of these unique magmas in lunar rocks.
