A team from US, France, U.K. is reporting data sent back by Mars rover Curiosity suggests Mars may have once had a continental crust similar to Earth. They describe 20 rocks that had been probed by the rover, and why their findings suggest a different history for the planet than has been thought. Researchers believe they have found evidence that suggests that rather than a lack of magmatic planetary activity, which should have been evident in rock samples showing mostly basalt, rock samples are full of silica and have a rich composition.
The light-colored rock samples are from an area inside the Gale Crater (in the southern hemisphere near Mount Sharp) and have been dated back to approximately 3.6B years ago. The researchers describe the rocks as looking like mineral composition samples taken from Earth, a huge departure from the dark basilica that was expected >> suggests planet may once have experienced plate tectonics similar to that on Earth. Up until now, the assumption has been that Mars did not have magmatic activity, which it is believed necessary for development of plates. That would have left the surface covered with basalt, similar to the situation at the bottom of our own world’s oceans, but of the rocks the ingredients are actually very similar to some of the oldest continental materials on Earth.
The rock samples could have come to be the way they are, for example, by the partial melting of basalts as they sank back into the crust. As always, more research will be needed to truly understand the history of the rocks.
{ SPECIMENS: 22 analysed by Curiosity that demonstrate that these light-toned materials are feldspar-rich magmatic rocks. The rocks belong to 2 distinct geochemical types: alkaline compositions containing up to 67 wt% SiO2 and 14 wt% total alkalis (Na2O + K2O) with fine-grained to porphyritic textures on the one hand, and coarser-grained textures consistent with quartz diorite and granodiorite on the other hand. The analysis reveals unexpected magmatic diversity and the widespread presence of silica- and feldspar-rich materials in the vicinity of the landing site at Gale crater. Combined with the identification of feldspar-rich rocks elsewhere and the low average density of the crust in the Martian southern hemisphere, they conclude that silica-rich magmatic rocks may constitute a significant fraction of ancient Martian crust and may be analogous to the earliest continental crust on Earth. }
http://phys.org/news/2015-07-curiosity-continental-crust-mars.htmljCp
Diversity of rock textures. Credit: Nature Geoscience (2015) doi:10.1038/ngeo2474
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