(ORDO NEWS) — American geochemists for the first time analyzed the isotopic composition of sulfur in samples collected during the Apollo 15 and Apollo 17 lunar missions. The results showed that the geological history of the Moon was rather turbulent. The article was published in the journal Science Advances.
Variations of sulfur isotopes in lavas of mantle origin can tell a lot about the stages of evolution of planetary bodies. While these isotopic ratios are well known for terrestrial igneous rocks, they have not yet been studied in detail in lunar rocks.
Alberto Saal of Brown University in Providence and Erik Hauri of the Carnegie Institute of Science in Washington DC made the first measurements of the 34S / 32S sulfur isotope ratio in volcanic glasses and olivine melt inclusions. All previous researchers have determined sulfur isotope ratios only in bulk rock samples, which are very difficult to draw any conclusions from.
The authors found isotope signatures indicating several important events in the geological history of the Moon: first, the lunar core was released and an ocean of lunar magma was formed, then this ocean froze, and heterogeneous magma chambers were formed at depth. With their activation, volcanic eruptions began – the outpouring of lavas, the release of pyroclastic, clastic material and the release of volcanic gases. This completes the process of fractionation of sulfur isotopes.
Despite the fact that this does not answer the main question necessary to understand the history of the origin of the Moon – whether the interior of the Earth and the Moon have the same signature of a sulfur isotope – the results of the new study are an important step towards solving this puzzle, scientists say. It is now at least clear that the Moon, like the Earth, went through stages of magmatic differentiation and degassing.
To better understand the processes that control changes in sulfur isotope ratios, the researchers used the latest nanoscale secondary ion mass spectrometry (NanoSIMS), which measures individual balls of volcanic glass and the smallest inclusions.
The studied samples are represented by two main types of lunar volcanic rocks: the so-called marine basalts, which fill the lunar seas, and pyroclastic deposits, rich in volcanic glass. Both exhibit wide variations in titanium content.
Scientists have found a clear correlation between the values of sulfur isotopes and the titanium content in magmatic liquid droplets enclosed in olivine crystals, as well as a positive relationship between the sulfur content in the samples and its isotopic values.
The authors suggest that these correlations arose in the process of the release of magmatic gases during volcanic activity, which produced marine basalts that formed after the formation of the primary lunar crust.
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