Curiosity finds rocks that might point to a continental crust on Mars

July 14, 2015 by Bob Yirka, Phys.org report
Diversity of rock textures. Credit: Nature Geoscience (2015) doi:10.1038/ngeo2474

(Phys.org)—A team of researchers from the U.S., France and the U.K. is reporting that data sent back by the Mars rover Curiosity suggests that the Red Planet may have once had a continental crust similar to that found back here on planet Earth. In their paper published in the journal Nature Geoscience, the team describes their analysis of data describing 20 rocks that had been probed by the rover, and why their findings suggest a different history for the planet than has been thought.

With all the excitement and news coming from the New Horizons probe as it conducts a flyby of Pluto, it is easy to forget that the Mars rover Curiosity is still active and still sending back valuable information. In this latest bit of news, researchers studying data sent back from the probe 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 3.6 billion years ago. The researchers describe the rocks as looking like mineral composition samples taken from Earth, a huge departure from the dark basalt that was expected. The similarity suggests the 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 would have been necessary for the 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. The researchers note that for some of the rocks the ingredients are actually very similar to some of the oldest continental materials on Earth.

Igneous clast named Harrison embedded in a conglomerate rock in Gale crater, Mars, shows elongated light-toned feldspar crystals. The mosaic merges an image from Mastcam with higher-resolution images from ChemCam's Remote Micro-Imager. Credit: NASA/JPL-Caltech/LANL/IRAP/U. Nantes/IAS/MSSS.

The findings do not confirm magmatic activity on the planet or the existence of tectonic plates, the researchers acknowledge, they simply suggest it might have been a possibility. The 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.

Explore further: Geologic study suggests Earth's tectonic activity peaked 1.1 billion years ago

More information: In situ evidence for continental crust on early Mars, Nature Geoscience (2015) DOI: 10.1038/ngeo2474

Abstract
Understanding of the geologic evolution of Mars has been greatly improved by recent orbital, in situ and meteorite data, but insights into the earliest period of Martian magmatism (4.1 to 3.7 billion years ago) remain scarce9. The landing site of NASA's Curiosity rover, Gale crater, which formed 3.61 billion years ago within older terrain, provides a window into this earliest igneous history. Along its traverse, Curiosity has discovered light-toned rocks that contrast with basaltic samples found in younger regions. Here we present geochemical data and images of 22 specimens analysed by Curiosity that demonstrate that these light-toned materials are feldspar-rich magmatic rocks. The rocks belong to two 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. Our 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, we 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.

Press release

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Returners
1.6 / 5 (5) Jul 14, 2015
I think some consideration needs to be given to the fact rocks would form differently on Mars due to lower gravity at the surface, and therefore lower internal pressures as well. Pressure and internal heat play a huge role in determining the types of minerals and rocks which can form even in the presence of the same chemistry. Also, rock forming in a hydrated environment would behave differently than that in a dry environment. Mars was supposedly wet in its ancient history, according to most accepted theories; who knows whether true or not, as it's a "faint young Sun" paradox all over again, as the solar radiation should have been less, but the planet coudl have been warmer from accretion and radiologically to make up for the difference.

I wouldn't expect the internal structure of granites or diorites on Mars to be identical to that on Earth due to the gravity and pressure differences.
Physphan
4.2 / 5 (5) Jul 14, 2015
I don't know why scientists that spend their life studying these things didn't think of that. Thanks, Returners!
Torbjorn_Larsson_OM
5 / 5 (3) Jul 15, 2015
@Returners: Yeah, did you think they didn't account for the gology in their geology? It is as if you hadn't read the paper, but are purposelessly trolling.

Oh, and "who knows whether true or not": We. We know. It is an (arguable) observation.
mreda14
5 / 5 (1) Jul 16, 2015
What a great discovery. Indeed this what I call the the nano science age.
ciprian
not rated yet Jul 17, 2015
Wow, just looking at the texture of these rocks may point against the conclusion. They actually presented the analysis of some feldspar laths in a dark matrix... Neither of these textures presented recalls a TTG. Usually when you make a rock classification one takes the bulk volumetric composition not the individual microscopic shots shown here. Where is quartz supposed to be here? TTG series all have quartz. It would take more than 89 shots to convince any decent petrologist that we deal with a continental rock. BTW how you define continents on Mars?
This is enough to make petrology students not pass an exam while on Mars one can publish in Nature... Odd world.

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