P54B-08:
Hypotheses on the Source of Potassium Enrichment in Some Gale Crater Rocks
Abstract:
K2O contents of rocks and soils were measured or estimated with three instruments on Curiosity in Gale Crater, Mars: ChemCam (laser induced remote sensing), APXS (α-particle X-ray spectroscopy), and CheMin (X-ray diffraction analysis). In some sedimentary rocks the K2O contents are consistent with the rock’s mineralogy, but in others K2O is higher than expected for the mineralogy. We have considered five hypotheses for the high abundance of K2O in Gale Crater sediments.Hypothesis I; K2O is enriched in plagioclase feldspar due to crystallization at high temperatures and pressures. Hypothesis II, some sedimentary rocks are enriched in K2O-rich feldspars. Hypothesis III; rocks may have been enriched in K2O by secondary mineral formation. Hypothesis IV; dust has been incorporated into the rocks. Hypothesis V, K2O is contained in an amorphous or a nanocrystalline phase. Hypotheses IV and V are easily invalidated because the measured and inferred compositions of dust and amorphous and nanocrystalline material are not sufficiently enriched in K2O to cause the observed K2O in sedimentary rocks.
Hypothesis I is possible because high-K2O plagioclase feldspars are sometimes observed in martian meteorites and sediments may have incorporated feldspars of these compositions. Hypothesis II is supported if potassium-rich feldspars, which have been identified by XRD of Gale Crater sediments and have been found in some martian meteorites, are concentrated in Gale sediments by fluvial processes. Hypothesis III is supported if correlations of K2O with other components of alteration minerals or secondary phases are found such as in a K2O-rich phyllosilicate, jarosite, alkali feldspar, or a potassium and fluorine-bearing phase.
Hypotheses I and II may explain the elevated K2O in Gale Crater sediments, however, potassium enrichments must be compatible with mineralogy. Hypotheses III is supported if a K2O-rich secondary phase or phases can be identified. The cause of K2O enrichment could reveal much about past igneous, geochemical, and physical processes in Gale Crater.