The Mineralogy of Lithic Components Within the North Polar Layered Deposits of Mars
The geology of the north polar plateau, Planum Boreum, and the surrounding dune fields in the north polar region of Mars has been of interest to the Mars community, as the ice-rich and sedimentary deposits in and around Planum Boreum record the recent sedimentary and climatic history of Mars. The NRC Planetary Science Decadal Survey (2011) identifies the polar regions of Mars as high priority targets for investigation and recommends a north polar lander mission to sample ice cores on the north polar layered deposits (NPLD), to constrain the past climate and geologic processes. However, linking the geologic record at the north pole to the history of the climate will require quantitative age dating of the NPLD, which can only be applied to non-ice lithic materials. Thus, in this study we aim to answer a very important question, “Are datable materials present within the NPLD?”. This study was completed as a part of NASA’s Mars Data Analysis Program, and aims to assess the composition of lithic components within NPLD and thereby constrain the geologic processes actively contributing to its formation. Lithics in the NPLD have previously been hypothesised to be composed of airfall martian dust. In this study, we test the bulk composition of the layered deposits for the presence of other datable primary minerals deposited on the NPLD after formation in impact or volcanic events (e.g., pyroxenes, Fe-bearing glass, etc.), which if detected, will be useful in constraining the geological processes aiding ice and sediment accumulation on Planum Boreum. This study is carried out using hyperspectral CRISM MTRDR data products which are already corrected for atmospheric, photometric and instrumental effects. The analysis is performed using the ENVI software package in conjunction with the CRISM Analysis Toolkit. Spectral summary parameters are used to to qualitatively measure the shape of the spectra to detect various Fe-absorption indicative of primary mafic minerals. These summary parameters are used to generate RGB composite maps to assess the variability in mineralogy at the site of investigation, and to guide detailed spectral analysis to determine the mineralogy of specific units within Planum Boreum. Results of this analysis show there is a significant concentration of lithics other than ferric dust throughout the NPLD. The most dominant material observed is glass, suggesting sources such as microtektites from distant impacts or phreatomagmatic ash. As we see that the glass forming processes are dominant on Mars, the rate of distant impacts and phreatomagmatic volcanism directly influence the accumulation rate of NPLD. Therefore, by factoring these geological constraints in the climate models, a better estimate on the age of NPLD can be obtained. In addition, the presence of likely impact and volcanic layers within Planum Boreum makes this region an excellent site for a future polar lander to quantitatively determine the age of deposit, thereby constraining the timing of ice deposition. Having such time constraints will be crucial for establishing correlations with the climatic records contained within the NPLD and enable greater understanding of the evolution of the planetary environment during the Amazonian on Mars.
Horgan, Purdue University.
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