Mapping Mars geochemically

Using multivariate cluster analysis, we identify six distinct geochemical provinces on Mars from the concentrations of K, Th, Fe, Si, Ca, Cl, and H 2 O determined by the Mars Odyssey gamma ray spectrometer. The results show that the Martian surface is dominated by basaltic rocks that vary in their abundance of incompatible (K, Th) and major elements (Fe, Si, and Ca). These chemically distinct geochemical provinces are in large, contiguous regions comprising a mixture of geologic units. The K/Th ratios are uniform among the geochemical provinces. To prevent measurable fractionation of K from Th, aqueous events must have been brief and/or the total throughput of water small. The muted weathering effects led to deposition of younger sedimentary deposits with the same compositions as older igneous units, explaining why a geochemical province may contain mapped units with the same composition but a range of ages.

[1]  Joshua L. Bandfield,et al.  A Global View of Martian Surface Compositions from MGS-TES , 2000 .

[2]  J. Head,et al.  Northern lowlands of Mars: Evidence for widespread volcanic flooding and tectonic deformation in the Hesperian Period , 2002 .

[3]  G. J. Taylor,et al.  Kinetic model of olivine dissolution and extent of aqueous alteration on mars , 2006 .

[4]  R. Reedy,et al.  The Martian Surface: Elemental abundances determined via the Mars Odyssey GRS , 2008 .

[5]  T. Encrenaz,et al.  Mars Surface Diversity as Revealed by the OMEGA/Mars Express Observations , 2005, Science.

[6]  Ronald Greeley,et al.  Geologic map of the eastern equatorial region of Mars , 1987 .

[7]  P. Rousseeuw.  Silhouettes: a graphical aid to the interpretation and validation of cluster analysis , 1987 .

[8]  G. J. Taylor,et al.  Possible ancient giant basin and related water enrichment in the Arabia Terra province, Mars , 2007 .

[9]  Richard D. Starr,et al.  Concentration of H, Si, Cl, K, Fe, and Th in the low- and mid-latitude regions of Mars , 2007 .

[10]  Scott M. McLennan,et al.  Acid-sulfate weathering of synthetic Martian basalt: The acid fog model revisited , 2004 .

[11]  Robert Haining,et al.  Spatial data analysis , 2003 .

[12]  J. Bandfield,et al.  Global spectral classification of Martian low-albedo regions with Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) data , 2007 .

[13]  K. Kojima.  Proceedings of the fifth Berkeley symposium on mathematical statistics and probability. , 1969 .

[14]  S. McLennan,et al.  A ∼3.5 Ga record of water-limited, acidic weathering conditions on Mars , 2007 .

[15]  Raymond E. Arvidson,et al.  Global thermal inertia and surface properties of Mars from the MGS mapping mission , 2005 .

[16]  F. Nimmo.  EARLY CRUSTAL EVOLUTION OF MARS 1 , 2005 .

[17]  S. Squyres,et al.  Mars Exploration Rovers - Chemical composition by APXS , 2008 .

[18]  Harry Y. McSween,et al.  Spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of Mars , 2002, Nature.

[19]  D. H. Scott,et al.  GEOLOGIC MAP OF THE WESTERN EQUATORIAL REGION OF MARS , 1986 .

[20]  William V. Boynton,et al.  Geochemistry of Martian soil and bedrock in mantled and less mantled terrains with gamma ray data from Mars Odyssey , 2007 .