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| Titel |
Representative composition of the Murray Formation, Gale Crater, Mars, as refined through modeling utilizing Alpha Particle X-ray Spectrometer observations |
| VerfasserIn |
Scott VanBommel, Ralf Gellert, Jeff Berger, Elstan Desouza, Catherine O'Connell-Cooper, Lucy Thompson, Nicholas Boyd |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250146619
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| Publikation (Nr.) |
 EGU/EGU2017-10652.pdf |
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| Zusammenfassung |
| The Murray formation[1] in Gale Crater is distinctly characterized by depleted MgO and CaO,
an elevated Fe/Mn ratio, and enrichments in SiO2, K2O, and Ge, compared to average Mars.
Supported by observations with Curiosity’s Alpha Particle X-ray Spectrometer[2], this pattern
is consistent over several kilometers. However, intermixed dust, Ca-, and Mg-sulfates
introduce chemical heterogeneities into the APXS field of view. Better constraints on
the composition of what is characteristic of the Murray formation is achieved by
applying a least-squares deconvolution[3] to a selection of APXS Murray targets. We
subtract the composition of known additions (dust[4], MgSO4, CaSO4) to derive a
more-representative Murray composition. Slight variations within Murray are then probed by
modeling each target as a mixture of dust, sulfates and the derived representative
Murray.
The derived composition for what is representative of Murray has several key deviations
from the straightforward average of Murray targets. The subtraction of known dust, Mg-, and
Ca-sulfate additions suggests further depletion in MgO and CaO in Murray and also
suggests a significant decrease in SO3 concentration compared to the average of
Murray targets. While veins and concretions are contaminants when considering the
composition of the bulk rock, the subtraction of Mg- or Ca-sulfate is independent of
sulfate form. Sulfates within the bulk rock (detrital or cements) have been observed
in the Murray formation. These sulfates are important and discussed further in
[5].
Modeling APXS Murray targets as a mixture of dust, MgSO4, CaSO4, and
representative Murray, provides insight into potential subtle variations within the
surprisingly consistent Murray formation. For example, the high SiO2 in Buckskin, (sol
1057-1091) is not simply a mixture of representative Murray with sulfates and dust. The
elevated Ni (and MgSO4) of Morrison (sol ∼775), the elevated Al2O3 of Mojave
(sol ∼800-900), and the gradually increasing Fe/Mn ratio (by decreasing Mn with
near-constant FeO) all stand out from this modeling. The constant CaO, after the
impact of CaSO4 is removed, as well as the steady SiO2, TiO2, and FeO, aside from
Buckskin, are also clearly visible. Along the traverse up Mount Sharp, there also
is an apparent downward trend in Mn and Zn and an increasing trend in Cl and
Br.
The chemical homogeneity of the Murray formation encountered at Gale Crater provides
an opportunity to test existing algorithms in new ways. This homogeneity along the traverse
is a major finding in itself, however, removing signals of known additions and deriving a
composition representative of the Murray formation, is important as it permits the potential to
detect and quantify faint variations within the Murray formation as Curiosity continues up
Mount Sharp.
References:
[1] Grotzinger et al. (2015) Science, 350 (6257). [2] Gellert and Clark (2015) Elements,
11, 39-44. [3] VanBommel et al. (2016) XRS, 45(3), 155-161. [4] Berger et al. (2016) GRL,
43 67-75. [5] Thompson et al. (2017) LPSC XLVIII 3020.
Acknowledgements:
This work has been supported by the Canadian Space Agency (CSA) under contract
9F052-14-0592. The MSL APXS is financed and managed by the CSA with MacDonald
Dettwiler and Associates as the primary contractor to build the instrument. Funding is
provided by the CSA and NASA. Much appreciation goes to JPL for their support,
dedication, and invaluable expertise. |
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