Lunar rock samples reveal surprisingly modern volcanic activity on the Moon
Lunar samples returned by China’s Chang’E-5 mission in 2021 have revealed that the Moon was still seeing volcanic activity one billion years later than scientists previously thought.
The only samples available prior to this were those returned by the Apollo and Luna missions in late 1960s and 1970s that are all more than three billion years old. This led scientists to believe that the Moon has been geologically dead since then.
But a new study from the Institute of Geology and Geophysics of the Chinese Academy of Sciences (IGGCAS) using the newly acquired samples found that mantle melting-point depression due to the presence of fusible, easily melted components could generate young lunar volcanism.
For the small rocky Moon, the heat fuelling volcanic activity was expected to have been lost long before these eruptions two billion years ago.
Scientists previously speculated that either elevated water content or heat-producing elements in the lunar interior might have driven volcanism in the late stage of the Moon’s life. But the Chang’E-5 data recently published in Nature has ruled out these once-leading hypotheses.
“Recent melting of the lunar mantle can be achieved by either raising the temperature or lowering the melting point. To better understand this problem, we should estimate the temperature and pressure in which the young volcanism was created,” said Professor Chen Yi, leader of the study.
The researchers conducted a series of fractional crystallisation and lunar mantle melting simulations to compare 27 precious Chang’E-5 basalt clasts with Apollo basalts. They found that the young Chang’E-5-source magma had higher calcium oxide and titanium dioxide contents than older Apollo magmas.
“This is a fascinating result, indicating a significant contribution of late-stage lunar magma ocean cumulates to the Chang’E-5 volcanic formation,” said Dr Su Bin, first author of the study.
Because the late-stage lunar magma ocean cumulates are calcium-titanium-rich and more easily melted than earlier samples, adding these fusible components to the lunar interior through gravitationally driven mantle overturn could have efficiently reduced the mantle melting temperature and thus triggered the young lunar volcanism.
“We discovered that the Chang’E-5 magma was produced at similar depths but 80°C cooler than older Apollo magmas. That means the lunar mantle experienced a sustained, slow cooling of 80°C from some three billion years to two billion years ago,” Bin said.
This work presents evidence for the first viable mechanism to account for young volcanism on the Moon that is compatible with the newly returned Chang’E-5 samples, the researchers believe.
E&T recently looked at the methods and materials that engineers are currently testing to allow a base to be built on the Moon’s surface.
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