Martian meteorites are mostly volcanic in origin, but how they are related to one another and where they come from on Mars have been enduring scientific puzzles. These meteorites can be found in the hot and cold deserts of the Sahara and Antarctica, respectively.
In a new NASA-funded study, geologist James Day of the Scripps Institution of Oceanography at the University of California San Diego and his colleagues addressed these questions by examining 40 Martian meteorites for their chemical compositions.
The researchers found that two dominant types of Martian meteorites, known as shergottites and nakhlites, had complementary compositions. These relationships are like those observed in Hawaii between the composition of basaltic rocks from the active volcano of Kilauea and volcanic rocks like those found in Diamond Head Crater on Oahu.
The construction of the Hawaiian islands by a hot mantle plume and their immense weight create the distinctive volcanic rock types there. This massive weight then pushes down on the Pacific plate, leading to melting where the water-rich plate bends to form volcanoes like Diamond Head Crater. The researchers suggest the same origins for Martian volcanism. The findings were published on Nov. 15 in the journal Nature Communications.
“The relationship of Martian meteorites to one another has been a long-standing question for decades,” said Day, lead author of the study. “Our new results show a link between these diverse meteorites and also a strong similarity with volcanic processes that we observe on Earth.”
The “flexure,” or bending, of the Pacific plate by the formation of Hawaii is dwarfed by the processes acting on Mars. Olympus Mons is the largest volcano in the Solar System, some three times taller than Mt. Everest, and the massive load it places on the martian surface bends and warps it downward.
“This bending, or lithospheric flexure, can lead to immense stresses and can also lead to melting and volcanism, which is exactly what we see in Hawaii,” said Day. “Martian meteorites represent both the volcanic material forming the massive volcanoes, like Olympus Mons, and the small volcanoes occurring due to lithospheric flexure.” 
The relationship of Martian meteorites to one another also has implications for basaltic rocks examined by the Mars Exploration Rovers, including Spirit, which landed at Gusev Crater. There, the rocks are distinct from the majority of Martian meteorites, and the new study indicates an important role for melting of water-rich materials by tectonic processes to form rocks like the Gusev Crater basalts.
“The new model we propose for how Martian volcanic rocks form, both from the big volcanoes, and volcanic rocks associated by bending and flexing of the upper portions of Mars, can potentially explain the complete range of volcanism seen on Mars,” said Day.
Co-authors of the study include Kim Tait of the Royal Ontario Museum in Canada, Arya Udry of the University of Nevada Las Vegas, Frédéric Moynier of the Université Paris Diderot, Yang Liu of the Jet Propulsion Laboratory, California Institute of Technology, and Clive Neal of the University of Notre Dame.