Mars’ crustal evolution does not follow Earth’s formula
Mars, strewn with rocks and pocked by craters, may not have an Earth-like, continental crust. Instead, a Cornell scientist poses an alternative theory: Crystalized magma welled up from inside the red planet.
Three years ago, scientists published work based on data returned by the NASA rover Curiosity that drilled into the Martian surface near Gale Crater. The rover found “granite-like” rock that indicated a Martian continental crust similar to Earth.
But geology can be complicated. “To make continental crust you need to brew its ingredients for a very long time – millions and millions of years. The brewing process is complex, involving process of plate tectonics,” said CSI member Esteban Gazel, Cornell associate professor of earth and atmospheric sciences.
Gazel and colleagues from the University of Nevada, Las Vegas and the University of Tennessee saw no indication the Martian crust was formed by plate tectonics or a true continental crust. Their work, “Formation of Evolved Rocks at Gale Crater by Crystal Fractionation and Implications for Mars Crustal Composition,” published May 31 in the Journal of Geophysical Research: Planets.
The researchers studied the continental crust hypothesis. To simulate how magma forms igneous (volcanic) rocks, they used the thermodynamical software called MELTS. For starting composition data, the team used a Martian meteorite that fell to Earth and five Mars surface rocks – Fastball, Backstay, Esperanza, Home Plate June Emerson and Champagne – visited by the NASA rover Spirit. (Steve Squyres, Cornell’s James A. Weeks Professor of Physical Sciences, was Spirit’s principal scientific investigator.)
The scientists realized that simple magma evolution – magma cools down and produces crystals, then changes in composition as new crystals form – would create a planetary crust through a process called fractional crystallization. That was a simpler geologic recipe revealed at the area surrounding Gale Crater. The group found that the “granite-like” rocks near Gale Crater do not constitute continental crust, analogous to Earth crust.
The magma evolutionary process is very common on Earth, said Gazel. “You can find it in Hawaii, Iceland or the Canary Islands. Volcanoes from these locations also produce magma that has high-silica content, but it does make it a continental crust. Although this magma has high amounts of silica, the magma lacks the remaining ingredients,” he explained. “This is just a natural process that happens in Earth’s volcanoes too, and it doesn’t necessarily make new continents.”
As an analogy, Gazel explained that the granite used to make kitchen countertops is created through an accumulation of crystals in a magma chamber. “You cannot have kitchen countertops if, in previous geologic processes, magma does not cool down,” he said. “That process is called fractional crystallization, resulting in the compositions commonly found on Mars.
“Nevertheless, our study confirms the formation of Mars’ early magmas by activity similar to processes found in Hawaii today,” Gazel said. “There are gigantic upwellings of hot mantle material from deep regions in Mars.”
Gazel’s co-lead author was Arya Udry of the University of Nevada, Las Vegas and also the study included a collaboration with Harry Y. McSween Jr. of the University of Tennessee.
This research was supported by NASA and the National Science Foundation.
Story by Blaine Friedlander (from July 19 2018)
Esteban Gazel, Earth & Atmospheric Sciences