Scientists say the mineral is tridymite, a form of quartz that forms at high heat and low pressure and is extremely rare on Earth, but they haven’t figured out how it got there on Mars.
Scientists chose Gale Crater as the landing site for NASA’s Curiosity because it may have contained ancient liquid water. The craft recently discovered evidence that Gale Crater was a lake a billion years ago.
“The discovery of tridiimide in rock is new,” said Christine Seebach, an associate professor in Rice University’s Department of Earth, Environmental and Planetary Sciences, co-author of the study published online in the journal Earth and Planetary Science Letters and a mission specialist on NASA’s Curiosity team, the most surprising of Curiosity’s 10-year Mars mission. One of the observations was the mud in Gale Crater.
He added: “Tridymite is usually associated with developed and eruptive volcanic systems composed of quartz on Earth, but we found it at the bottom of an ancient lake on Mars, where most of the volcanoes are very old.”
The team reviewed volcanic material from samples of Martian volcanoes and re-examined sediment evidence from Gale Lake. They came up with a new scenario that fits all the evidence: Martian magma stayed in a chamber beneath the volcano for longer than usual, undergoing a partial cooling process called microcrystallization until more silicon became available.
In a major eruption, the volcano spewed additional silicon-rich ash over the Tridemite into Gale Crater Lake and surrounding rivers.
The water helped break down the ash through the natural processes of chemical weathering, and it also helped sort the weathered minerals.
This scenario is also illustrated by other geochemical evidence in the sample, including opaline silicate and low concentrations of aluminum oxide.
“It’s actually a direct evolution of other igneous rocks that we’ve found in the crater,” Seebach said. We only saw this mineral once, and it was so thick in one layer that we argue that the volcano probably erupted at the same time as the lake. Although the particular sample we analyzed is not volcanic ash, it is weathered and water-sorted ash.
If a volcanic eruption like the one in Gale Crater had a lake, it would mean that the volcanoes erupted 3 billion years ago when Mars was moving from a wetter and warmer world to a drier one. And barren nature it is today.
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