Areal Distribution of Potential Felsic Material in Nili Patera at Syrtis Major, Mars

Abstract:

For decades, studies of the exposed igneous Martian crust via remote sensing and landed observation have concluded that it is predominantly basaltic. However, new analyses of meteorites and mission data indicate a wider range of primary rock composition. Nili Patera in the Syrtis Major region provides one of the best exposures of evolved compositions. Recently, Wray et al. (2013) identified a new unit in the caldera with very high feldspar abundance but unusually low mafic abundance and interpreted it as a felsic unit (as opposed to spectrally similar anorthosite) based on its proximity to a dacite unit.

We investigate the summit calderas of Syrtis Major by defining and mapping distinct compositional units using mineralogies inferred from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter (MRO). The study focuses on the areal extent of potential felsic material, identified based on a broad absorption feature centered at ~1.25-1.3 μm, a unique feature of feldspars attributed to minor Fe²⁺ substitution. These mapping efforts are put in geologic context using images from the High Resolution Imaging Science Experiment (HiRISE) instrument on MRO and existing mapping efforts in the area, as well as spectral context using laboratory generated spectra of feldspar and mafic mixtures. While further work understanding this potential felsic unit is warranted, if it is truly felsic it implies a more complicated Martian magmatic history than previously thought. As the diversity of known geologic materials on Mars grows, it is necessary that we understand how to recognize and characterize those materials using the instruments available on current and upcoming missions, such as MRO or the Mars 2020 Rover. Through modeling and data analysis, our ongoing work seeks to understand the geophysical and petrologic context in which the potential felsic materials were generated, and thus to infer their implications for Martian magmatic history.

References: Wray, J.J. et al. (2013), Nature Geosci. 6, 1013-1017.