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The K and Th concentration in the Martian crust: insights from multi-scale analyses
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  • David Baratoux,
  • Fall Makhoudia,
  • Pierre-Yves Meslin,
  • Papa Moussa Ndiaye,
  • Lenka Baratoux,
  • Jean-François Moyen,
  • Mark Jessell,
  • Olivier Vanderhaeghe
David Baratoux
Université Félix Houphouët-Boigny

Corresponding Author:[email protected]

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Fall Makhoudia
University Cheikh Anta Diop
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Pierre-Yves Meslin
IRAP, Universite Paul Sabatier
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Papa Moussa Ndiaye
University Cheikh Anta Diop
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Lenka Baratoux
IRD Institute for Research and Development
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Jean-François Moyen
University of Saint-Etienne
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Mark Jessell
The University of Western Australia
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Olivier Vanderhaeghe
Geosciences Environnement Toulouse
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The univariate statistics of potassium (K) and thorium (Th) concentrations in the oceanic and continental crust of the Earth has been recently investigated from geochemical databases and airborne radiometric surveys [1]. This study demonstrates that the frequency distributions of these elements are scale-dependent. There are right-skewed for small-scale samples (typical volume of rocks analyzed for an individual sample in a dataset) but tend to be more symmetric for large-scale samples. The right-skewed behavior of K and Th is attributed to their incompatible behavior during partial melting or fractional crystallization. The scale-dependence and evolution toward normal distributions are a direct consequence of the central limit theorem applied to K and Th concentrations. The results of the results of this study may be applied to Mars, using the Mars Odyssey global maps of K and Th concentrations [2]. In light of available K, Th concentrations at the rock-scale (in-situ samples and martian meteorites), we infer that each “pixel” of these maps reflect a right-skewed distribution of K and Th concentrations at smaller-scales, where K and Th-poor rocks, such as basalts, are spatially dominant. In turn, K, and Th-rich rocks, such as those found by Curiosity at Gale crater [3], may occur globally, though their spatial extension must be limited to account for the values reported by Mars Odyssey. The global, but sparse occurrence of K, Th-rich rocks at the surface is consistent with a buried felsic crust, outcropping at the favor of tectonic or impact events. These conclusions will be discussed in the context of the inferred constraints about the structure of the martian crust from Insight data [4]. [1] Baratoux, et al., Earth and Space Science, in press. [2] Boynton et al. JRGP, doi:10.1029/2007JE002887. [3] Sautter et al. doi:10.1038/NGEO2474. [4] Knapmeyer-Endrun et al., Science, doi: 10.1126/science.abf8966