A group of researchers believe Mars could harbor deposits of the igneous rock granite. This theory has recently been strengthened by the discovery of feldspar; the material is found to constitute as much as 60 percent of the Earth’s crust, and is also a component of granite.
Mars Geology not as Simple as First Suspected?
The study – which aimed to establish whether the Red Planet was more geologically diverse than astronomers initially suspected – was published in the latest issue of the journal Nature Geoscience, and was supported by the NASA Mars Data Analysis Program.
According to the research findings, a large proportion of feldspar was discovered in an ancient volcano. The eruptive equivalent of granite, called rhyolite, is typically identified on Earth in tectonically active regions where one tectonic plate moves under another, before sinking into the mantle; this region is called a subduction zone. The researchers consider this contingency to be remote and, instead, posit that the ancient magmatic activity of Mars might have been responsible for generating the composition of the Martian minerals.
Although felsic rocks – rich in feldspar and quartz – are found in large quantities within the Earth’s upper crust, they do not appear to be widely distributed across Mars. This point is reflected upon by the research authors in their latest study:
“Rocks dominated by the silicate minerals quartz and feldspar are abundant in Earth’s upper continental crust. Yet felsic rocks have not been widely identified on Mars, a planet that seems to lack plate tectonics and the associated magmatic processes that can produce evolved siliceous melts on Earth.”
For a long time, Mars was considered a baron, geologically simplistic planet, harboring mostly one type of rock. Spacecraft and meteorite data previously suggested that the
Martian surface is principally composed of dark-colored tholeiitic basalt, with much of the planet covered by small grains of iron oxide dust. Amounts of a magnesium iron silicate, called olivine, have also been found, alongside hematite; however, such deposits are identified infrequently and at very low concentrations.
Astronomers were shocked to find the presence of Martian soils that had compositions similar to granite. The astonishing discovery was made by the Mars Curiosity rover and has been puzzling the minds of scientists, ever since. Due to its limited abundance, confined to a single known region of the planet’s surface, some researchers were unsure as to the significance of the finding.
Assistant Professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, and lead author of the new study, James Wray, claims that his research team has yielded the “most compelling” evidence yet that Mars boasts granitic rocks.
Feldspar Found in Ancient Volcano
The team report near-infrared spectral data from the Compact Reconnaissance Imaging Spectrometer, onboard the Mars Reconnaissance Orbiter (MRO) for felsic rocks from three different sources across the Martian terrain.
One such area of interest was a large volcano, which was originally active for billions of years, before entering a stage of dormancy. The researchers report that the volcano was ideal for investigation, since it is subjected to high-speed sand dunes and remains dust-free.
Wray expressed the team’s surprise upon learning that the inside of the volcano was home to rich deposits of feldspar:
“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.”
The researchers found that the interior of the ancient volcano was mostly devoid of dark materials. This, along with the location of the feldspar deposits, provided researchers
potential insight into the process by which granite could form on Mars. Whilst the molten rock gradually cools in the subsurface, low density melt separates out from dense crystals, during a phenomenon known as fractionation.
Josef Dufek, associate professor in the School of Earth and Atmospheric Sciences, also based at the Georgia Institute of Technology, ran a series of computer simulations to explain how the repeated cycles of fractionation could result in the melt becoming enriched in silica; the melt then becomes lower in density and gains the physical properties of granite.
During a recent press release, Dufek compares the similarity in composition between the formations found in the Martian volcano with those seen in the volcanoes of Earth:
“These compositions are roughly similar to those comprising the plutons at Yosemite or erupting magmas at Mount St. Helens, and are dramatically different than the basalts that dominate the rest of the planet.”
Intriguingly, another study that was published in the same edition of Nature Geoscience, offered a different interpretation of the feldspar-rich deposits. Looking at a different location on the illustrious Red Planet, researchers from the European Southern Observatory and the University of Parks concluded the rocks to be more comparable to anorthosite, an igneous rock that is also commonplace on the moon. However, based upon the location of their discovery, Wray considers his research group’s theory, regarding granite formation, to be more likely.
Nonetheless, it certainly appears that Mars is far more diverse than researchers initially imagined. However, Wray calls for more research to be conducted into the history of volcanism of the ever-mysterious planet, in the hope that we might learn more about the different kinds of rocks that have been forming across Mars.
By James Fenner
Georgia Tech Press Release