FELDSPAR ON MARS THROUGH THE EYE OF A VISIBLE NEAR-INFRARED SPECTROMETER

Data from the Curiosity rover, as well as the Martian meteorite Northwest Africa (NWA) 7533 and its paired meteorites [1], presented groundbreaking evidence towards magmatic diversity in Martian rocks; raising questions towards the formation processes of the Martian crust [2]. The Curiosity rover found feldspar-rich rocks evolved in composition presenting SiO2 contents higher than 53%. The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter detected feldspar-bearing units in Noachian terrains (older than 3.8 billion years old) in the Southern Hemisphere including some of evolved composition [3-4], but their petrology is still unknown due to the lack of sub-cm images and complete chemical composition data. Constraining the spectral signature in CRISM spectral range of feldspar would better constrain the petrology of the feldspar-bearing Noachian terrains, which would enlighten us towards early crustal processes.

We used visible near-infrared spectroscopy to determine how various proportions of pyroxene and feldspar alter the spectral signatures of feldspar at various grain sizes. Feldspar can be identified with a broad absorption center between 1.1-1.3 µm due to Fe2+ substituting Ca2+ in the crystal lattice. We found that under the presence of mafic minerals including pyroxene, feldspar’s spectral signal is overridden, as expected according to [5]. Our results also show that the grain-size of feldspar contributes to the feldspar spectral behavior in the presence of mafic minerals at the same grain size, especially shifts in feldspar absorption center towards shorter wavelengths. Future work will include SEM analyses on augite and plagioclase samples and the mixtures in their various grain sizes to explore any chemical effects on the spectral behavior of feldspar within the mixtures.

1. Humayun et al. (2013). Nature, 503(7477), 513-516. 2. Sautter et al. (2015). Nature Geoscience, 8(8), 605-609. 3. Wray et al. (2013) Nature Geoscience, 6(12), 1013-1017. 4. Payré et al. (2022) GRL, 49(21). 5. Rogers and Nekvasil (2015), GRL, 42, 2619–2626.