11:00 AM - 11:15 AM
[PPS06-07] Origin of Mars feldspathic rocks from remote sensing data analyses and terrestrial analogue studies
★Invited Papers
Keywords:Mars, Plagioclase minerals, VNIR spectroscopy, Primary crust, Remote sensing, CRISM
Recent identification of feldspar signatures in Mars VNIR spectroscopic data raise questions about the origin of the host rocks. Initial interpretations leaned towards the presence of anorthositic rocks from an early (primary), lunar-like, floatation crust (e.g., Carter and Poulet, 2013). Alternatively, these rocks could correspond to later magmatic products (secondary crust, e.g., Wray et al., 2013; Rogers and Farrand 2022), or even to remnants of a continental (tertiary) crust (Sautter et al., 2015, 2016). The nature of the feldspar-bearing rocks remains enigmatic but has strong implications for the nature and origin of Mars’ crust.
Plagioclase feldspars can virtually be identified with spectroscopic techniques due to a 1.3 microns absorption in the VNIR domain (e.g., Adams and Goullaud, 1978; Cheek and Pieters, 2014), although their detection is not straightforward. Numerous uncertainties regarding the effect of feldspar composition, mineral mixtures and grain size persist (e.g., Barthez et al., 2023). The present project aims at investigating Mars’ crust composition by improving the analysis of remote sensing data and combining it with laboratory investigations of terrestrial analogs.
At the conference, we will present signatures observed with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument onboard Mars Reconnaissance Orbiter, and the associated geological context for new plagioclase detections made in the wall of Valles Marineris. The identification of weak plagioclase absorptions was made possible thanks to the use of a newly developed denoising algorithm, Mineral Recognizer, which greatly improves the CRISM signal/noise (e.g., Payet et al., 2020; Flahaut et al., 2023). The plagioclase absorption characteristics will be plotted against other, sparse detections recently made on Mars (e.g., Payré et al., 2022; Phillips et al., 2022). These plagioclase-like signatures will further be compared with those of potential analog feldspathic and felsic rocks (granitoids, TTG, anorthosites, gabbros, phenocryst basalts…) that were measured with both a fieldspec4 point spectrometer (which provides an average rock spectrum) and Hyspex VNIR and SWIR hyperspectral cameras (which allow grain to grain analysis) in our laboratory (https://crpg.univ-lorraine.fr/en/hyperspectral-remote-sensing-en/). We demonstrate that both on Mars, and in our rock collection, the signature of plagioclase has variable characteristics (band center, band width) which suggest varying chemical compositions and/or mineral assemblages. Coupled with high resolution imagery, our results show that the detections made on Mars likely correspond to diverse lithologies and geological contexts. Laboratory analyses of terrestrial analog rocks further demonstrate that several rocks could correspond to the observed plagioclase signatures, and that these lithologies do not need to be very rich in plagioclase to show a diagnostic 1.3 microns spectral feature. In contrast, plagioclase detection depends mostly on 1) the plagioclase grain size, and 2) the other minerals nature and relative grain sizes. Analyzed terrestrial rocks however often display both microscopic and spectral evidence for aqueous alteration, therefore new ongoing experiments focus on the measurements of less weathered Martian meteorites, and of synthetic plagioclase crystals.
Plagioclase feldspars can virtually be identified with spectroscopic techniques due to a 1.3 microns absorption in the VNIR domain (e.g., Adams and Goullaud, 1978; Cheek and Pieters, 2014), although their detection is not straightforward. Numerous uncertainties regarding the effect of feldspar composition, mineral mixtures and grain size persist (e.g., Barthez et al., 2023). The present project aims at investigating Mars’ crust composition by improving the analysis of remote sensing data and combining it with laboratory investigations of terrestrial analogs.
At the conference, we will present signatures observed with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument onboard Mars Reconnaissance Orbiter, and the associated geological context for new plagioclase detections made in the wall of Valles Marineris. The identification of weak plagioclase absorptions was made possible thanks to the use of a newly developed denoising algorithm, Mineral Recognizer, which greatly improves the CRISM signal/noise (e.g., Payet et al., 2020; Flahaut et al., 2023). The plagioclase absorption characteristics will be plotted against other, sparse detections recently made on Mars (e.g., Payré et al., 2022; Phillips et al., 2022). These plagioclase-like signatures will further be compared with those of potential analog feldspathic and felsic rocks (granitoids, TTG, anorthosites, gabbros, phenocryst basalts…) that were measured with both a fieldspec4 point spectrometer (which provides an average rock spectrum) and Hyspex VNIR and SWIR hyperspectral cameras (which allow grain to grain analysis) in our laboratory (https://crpg.univ-lorraine.fr/en/hyperspectral-remote-sensing-en/). We demonstrate that both on Mars, and in our rock collection, the signature of plagioclase has variable characteristics (band center, band width) which suggest varying chemical compositions and/or mineral assemblages. Coupled with high resolution imagery, our results show that the detections made on Mars likely correspond to diverse lithologies and geological contexts. Laboratory analyses of terrestrial analog rocks further demonstrate that several rocks could correspond to the observed plagioclase signatures, and that these lithologies do not need to be very rich in plagioclase to show a diagnostic 1.3 microns spectral feature. In contrast, plagioclase detection depends mostly on 1) the plagioclase grain size, and 2) the other minerals nature and relative grain sizes. Analyzed terrestrial rocks however often display both microscopic and spectral evidence for aqueous alteration, therefore new ongoing experiments focus on the measurements of less weathered Martian meteorites, and of synthetic plagioclase crystals.