Recent research has unveiled a crucial process in the formation of a distinctive lunar rock type, solving a longstanding puzzle in lunar geology. The study, published in Nature Geoscience, sheds light on the signature composition and origin of magmas found on the moon's surface, providing answers to questions that have perplexed scientists for decades.
The research, led by an international team of scientists from the University of Bristol in the UK and the University of Münster in Germany, delves into the intricate processes that led to the creation of unique lunar magmas known as 'high-Ti basalts.' These magmas, characterized by surprisingly high concentrations of titanium (Ti), were first discovered during the NASA Apollo missions in the 1960s and 1970s, which brought back solidified lava samples from the moon's crust.
The mystery surrounding these high-Ti basalts lay in their composition and how they managed to reach the lunar surface. The recent study employed a combination of high-temperature laboratory experiments using molten rocks and sophisticated isotopic analyses of lunar samples to identify a critical reaction that controls the composition of these magmas.
The key revelation centers around a reaction that occurred in the deep lunar interior approximately three and a half billion years ago. This reaction involved the exchange of iron (Fe) in the magma with magnesium (Mg) in the surrounding rocks, resulting in modifications to the chemical and physical properties of the melt. Co-lead author Tim Elliott, Professor of Earth Sciences at the University of Bristol, likens the process to an "avalanche" of an unstable, planetary-scale crystal pile created by the cooling of a primordial magma ocean.
"The origin of volcanic lunar rocks is a fascinating tale... It is great to have resolved this dilemma," says Professor Elliott. The research not only unravels the mystery of the high-Ti basalts' presence on the moon but also explains their unique characteristics, including their low density, allowing them to erupt billions of years ago.
Dr. Martijn Klaver, Research Fellow at the University of Münster Institute of Mineralogy and co-lead author, highlights the challenges faced by previous models in recreating the magma compositions matching the essential chemical and physical characteristics of high-Ti basalts. The recent study successfully addresses this gap by mimicking the high-Ti basalts in laboratory experiments, providing a comprehensive understanding of the melt-solid reaction integral to the formation of these magmas.