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Mars May Have Granite From Red Planet's Tumultuous Volcanic History
Mars's volcanic history may have been tumultuous enough to produce granite, a geologist interpreting a rock picked up by the Mars Rover said Sunday.
Although geologists already suspect that Mars might harbor granite, one team of geologists boasted in an online journal article that, "We're providing the most compelling evidence to date that Mars has granitic rocks." James Wray, an assistant professor at the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology and lead author of a study published in the Advance Online Publication of the journal Nature Geoscience, based the assertion on infrared spectroscopic analysis of a football-sized rock that the Mars Curiosity rover scooped up earlier this year.
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Although the Mars Curiosity rover didn't find granite itself, it did astonish geologists by harvesting rock from a large deposit of feldspar in an ancient inactive Martian volcano. Feldspar is a mineral found in granite, created by volcanic activity. "Prolonged magmatic activity on Mars can also produce these compositions on large scales," Dr. Wray said. "And we think some of the volcanoes on Mars were sporadically active for billions of years."
Before the rover started sending back data, geologists considered the Red Planet to be geologically simplistic, consisting mostly of basalt — the same type of dark volcanic rock that litters much of Hawaii. The presence of feldspar only in a volcano, and no where else on Mars, indicates to Dr. Wray that the feldspar is a result of volcanic activity involved in the forging of granite. Magma inside the volcano could have slowly cooled in one layer just below the surface, and dense crystals formed in another layer, he wrote.
If the cycle of the two layers heating and cooling repeated itself for millennia in the bowels of an active volcano, granite could form, according to the computer simulations Dr. Wray ran in collaboration with Josef Dufek, associate professor in the School of Earth and Atmospheric Sciences at Georgia Tech.
"In a volcano, you could get enough iterations of that reprocessing, that you could form something like granite," not unlike those formed by magma consolidation at Yosemite or erupting magmas at Mount St. Helens, Dr. Dufek said.
But not all geologists think that feldspar indicated granite. Another team of geologists, this one from the European Southern Observatory and the University of Paris, in the same edition of Nature Geoscience, found a similar signature elsewhere on Mars, but likens the rocks to anorthosite, a coarse-grained plutonic igneous rock consisting almost entirely of feldspar, and commonly found on the moon.
Whether through anorthosite or granite, the findings suggest the Red Planet is more geologically interesting than thought. The dynamic volcanic history on Mars, may have birthed rocks, said Dr. Wray, that are as "diverse on Mars, as they are on Earth."
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