Halogen clues shed light on lunar crust evolution

Halogen clues shed light on lunar crust evolution
by Robert Schreiber
Berlin, Germany (SPX) Jul 11, 2025

Rocks from the Moon's near side hold unexpectedly high levels of chlorine, offering fresh insights into the processes that shaped the lunar crust. An international team led by the University of Munster, alongside Ehime University in Japan and Vrije Universiteit Amsterdam, conducted lab-based simulations of lunar rock formation to explore how chlorine behaves under lunar conditions.

Their experiments, simulating the extreme heat and pressure of the Moon's early magma ocean phase, revealed how chlorine distributes between lunar minerals and melts. These findings help clarify how volatile elements, such as halogens like chlorine and fluorine, were incorporated into the Moon's crust.

The lunar surface is primarily composed of two rock types: bright, older highland anorthosites and younger, darker basaltic rocks. While both are found in similar proportions on the Earth-facing side, the far side lacks significant basaltic deposits. The cause of this asymmetric distribution remains uncertain.

"Our results show that chlorine is distributed in a very unusual way when lunar rocks melt," said Prof. Dr. Stephan Klemme from the University of Munster's Institute of Mineralogy. "It has been shown that rocks from the near-side of the Moon surprisingly contain a lot of chlorine, most likely as a result of volcanic eruptions, and chlorine-containing gases."

Interestingly, rocks outside the KREEP region-a zone rich in rare elements-do not exhibit elevated chlorine levels. "Analyses suggest that these rocks originate from a special part of the Moon that still preserves traces from the time of the Moon's formation," explained Dr. Jasper Berndt, also from the Institute of Mineralogy.

The team used high-purity chemicals mimicking lunar material, adding chlorine and subjecting the mixture to intense heat and pressure to replicate the Moon's interior. This approach enabled them to model how the primary lunar crust formed from the magma ocean and how chlorine became unevenly distributed.

The upcoming analysis of samples from China's Chang'e-6 mission, which returned material from the Moon's far side in June 2024, may offer critical data to verify whether similar chemical processes occurred across the entire lunar surface.

Research Report:Halogen abundance evidence for the formation and metasomatism of the primary lunar crust