Mud Volcanism Next LCROSS Northen Ice Cap Water was Global Nili FossaePublication of Joseph R. Michalski (1) and Paul B. Niles (2) in « Nature Geoscience » on Oct 10th 2010. (1)Planetary Science Institute, Tucson, Arizona/Institut d’Astrophysique Spatiale, Universite Paris Sud, Orsay, France. (2)Astromaterials Research and exploration Science, NASA, Johnson Space Center, Houston, Texas. We hereafter present hints at the content of this publication which is available (for a fee) on the website www.nature.com/naturegeoscience The study concerns the rocks of Leighton Crater (57°E / 3°N), close to Syrtis Major volcano which spread its lavas over the whole area, including the place where, later, an impact created the Leighton Crater. It was made on the basis of data gathered from CRISM (aboard Mars Reconnaissance Orbiter i.e. “MRO”) and OMEGA (aboard Mars Express) spectrometers as well as from the photos taken by the HiRISE camera (MRO).
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Evidence of carbonates in the deep crust of Mars Northern hemisphere.
Color HiRISE image of the central peak of Leighton Crater showing inter-layered carbonate (light colored) and chlorite (dark colored) units. These rocks suggest that inter-layered carbonate and clay sediments have been metamorphosed at depth due to hydrothermal conditions. Credit: NASA/JPL/University of Arizona
In this crater, large bands of kaolinites, carbonates and hydrated silicates, rich in iron and magnesium, have been identified. All those rocks imply a long interaction with water. The HiRISE camera shows that these rocks match the crater central peak and that they have therefore been exhumed from the bedrock underneath by the impact. Taking into account the size of the crater, the depth at which this bedrock lays is estimated to be about 6km.
A schematic diagram showing how impact craters can exhume materials from depth. The central peak of the crater represents material uplifted from depth, in this case approximately 6 km depth. In this image, THEMIS infrared data and OMEGA spectral data are draped over MOLA topography showing Leighton Crater in surface view, and in schematic view in the image cutaway. (The crater is ~65 km diameter, vertical exaggeration is 10x.) Credit: NASA/JPL/University of Arizona
One could wonder whether the hydration and the intense absorption of carbon occurred after the impact (and the surge of the rocks) or before. Taking into account the massive features of the phenomenon within the rocks of the peak and the fact that they are restricted to the rocks of the peak, this hydration should have occured before the impact and should concerns also the bedrock underneath the lava mantle from Syrtis Major. This bedrock is most likely made of siliclastic and volcanic sediments rich in carbonates which were before the surface of the planet, and subsequently were metamorphosed deep within the crust. Consequently, the time when the hydration took place is anterior to Syrtis Major volcanism (Hesperian). It is therefore during that very ancient period, that the atmosphere was thick enough to allow liquid water to be stable on the surface and allow the absorption of its carbon by the rocks which were soaked in it. Until now, we found little carbonates on Mars (in Nili Fossae area and in some outcrops of Columbia Hills, in Gusev crater). This new finding indicates that there should be much more under the extensive lava mantle which covers Northern Mars since the Teiikian era. This clearly confirms Professor Jean-Pierre Bibring’s theory according to which water was (in the Phyllocian period) abundant everywhere on the surface of Mars, and not only in the area where, at first glance, could have existed a boreal ocean (Vastitas Borealis). In reality, this “ocean” must have been only a “see” in the lunar meaning of the world i.e. an extended area of lava spread over the area at the time of the late massive bombardment of Mars (end of Noachian). It might have been later filled temporarily with water, at the time of the huge cataclysmic flows caused by the late tectonic activity and abundant volcanism of the Hesperian era but this water, even though it may have had an action the traces of which are still visible (estuaries, mud volcanism), did not stay long enough over the surface to deeply modify the rocks with which it was in contact. Obviously, this is a very interesting piece of information from an exobiological point of view. Pierre Brisson
Water