In fact, the rocks were silicate-rich.
"We've known for awhile that the Compton-Belkovich had an unusually high thorium content," Glotch said. "Now we can positively say that that thorium is related to these silicic volcano materials."
Volcanoes on the moon
Last fall, Glotch, working with another team, was the first to identify nonbasaltic volcanoes on the near side of the moon. Due to their highly reflective surface, this group was also originally noticed by the Lunar Prospector.
However, lava from the surrounding maria may have also concealed details of the volcanoes, so some details of the region's geologic history could have been hidden, researchers said. But the volcanoes on the far side have no maria nearby to hide their features. The complete view of the volcanism in the area lies open to examination.
Similarly, they are surprisingly free from impact craters, which reveals a great deal about their age, researchers added.
The early life of the solar system was violent, with rocks scarring the surface of the planets and their moons. Features that lack this scarring formed after things had calmed down.
Jolliff and his team estimated the age of the moon's rare far side silicate volcanoes to be about 800 million years old. Such an age would extend the volcanic activity of the moon by 200 million years, they said.
According to Glotch, the discovery of nonbasaltic volcanoes on the far side of the moon "shows that the moon is more compositionally diverse than we realized before this new age of lunar exploration."
"As scientists, we're still digesting all this relatively new data and working to understand what it means in terms of lunar history."
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