Gale Crater was chosen as Curiosity’s landing site because of the likelihood that it once contained liquid water, and indeed the rover found evidence that confirmed it was actually a lake 1 billion years ago.
This meant that finding tridymite in mudstones in the crater was surprising, as the mineral is usually associated with explosive, evolved volcanic systems on Earth that differ from the primitive volcanoes of Mars.
In the search for answers, the researchers re-evaluated data from every reported find of tridymite on Earth. They also examined volcanic material from models of volcanism on Mars and reexamined sedimentary evidence from Gale Crater Lake.
They then came up with a new scenario that matched all the evidence: Martian magma sat longer than usual in a chamber beneath a volcano, undergoing a partial cooling process called fractional crystallization, which concentrates silicon. In a massive eruption, the volcano ejected ash containing the extra silicon in the form of tridymite into Gale Crater Lake and surrounding rivers. The water helped break down the ash through natural processes of chemical weathering, and the water also helped sort the minerals produced by the weathering.
The scenario would have concentrated tridymite producing minerals consistent with the 2016 find. This would explain other geochemical evidence Curiosity found in the sample, including opaline silicates and reduced concentrations of alumina.
“This is actually a direct evolution of other volcanic rocks that we found in the crater,” study co-author Kirsten Seebach said in a media statement. “We argue that since we’ve only seen this mineral once and it was highly concentrated in one layer, the volcano probably erupted at the same time the lake was there. Although the particular sample we analyzed was not exclusively volcanic ash, it was ash that had been weathered and sorted by water.
If a volcanic eruption like the one in the scenario occurred when Gale Crater contained a lake, it would mean that explosive volcanism occurred more than 3 billion years ago as Mars was transitioning from a wetter and perhaps warmer world to a dry and barren planet it is today.
“There is ample evidence for basaltic volcanic eruptions on Mars, but it’s more advanced chemistry,” Siebach said. “This work suggests that Mars may have a more complex and intriguing volcanic history than we would have imagined before Curiosity.”
Add Comment