Scientists have found evidence of granite in an ancient Mars volcano and developed a new theory for how the igneous rock common on Earth could have formed on the Red planet.
The findings suggest a much more geologically complex Mars than previously believed, researchers say.
Large amounts of a mineral found in granite, known as feldspar, were found in an ancient Martian volcano. Further, minerals that are common in basalts that are rich in iron and magnesium, ubiquitous on Mars, are nearly completely absent at this location.
The location of the feldspar also provides an explanation for how granite could have formed on Mars. Granite, or its eruptive equivalent, rhyolite, is often found on Earth in tectonically active regions such as subduction zones.
This is unlikely on Mars, but the research team concluded that prolonged magmatic activity on Mars can also produce these compositions on large scales.
"We're providing the most compelling evidence to date that Mars has granitic rocks," said James Wray, from the Georgia Institute of Technology and the study's lead author.
For years Mars was considered geologically simplistic, consisting mostly of one kind of rock, in contrast to the diverse geology of Earth.
The new study bolsters the evidence for granite on Mars by using remote sensing techniques with infrared spectroscopy to survey a large volcano on Mars that was active for billions of years.
The volcano is dust-free, making it ideal for the study. Inside, the research team found rich deposits of feldspar, which came as a surprise.
"Using the kind of infrared spectroscopic technique we were using, you shouldn't really be able to detect feldspar minerals, unless there's really, really a lot of feldspar and very little of the dark minerals that you get in basalt," Wray said.
The location of the feldspar and absence of dark minerals inside the ancient volcano provides an explanation for how granite could form on Mars.
While the magma slowly cools in the subsurface, low density melt separates from dense crystals in a process called fractionation. The cycle is repeated over and over for millennia until granite is formed.
This process could happen inside of a volcano that is active over a long period of time, according to the computer simulations run in collaboration with Josef Dufek, who is also an associate professor in the School of Earth and Atmospheric Sciences at Georgia Tech.
The study was published in the journal Nature Geoscience.