Mapping feldspar-bearing rocks in Altiplano-Puna volcanic complex using EO-1 Hyperion for Mars analog study

1. Introduction

Located in northern Chile's central Andean region, the Altiplano-Puna volcanic complex is a province characterized by stratovolcanoes, ignimbrites, domes, and other volcanic features with composition ranging from basaltic andesite to dacite [1]. This region, along with its vicinity, possesses unique environments comparable to some planetary bodies due to its arid climate, volcanic terrain, and hydrothermal activities, and it has particularly been used as analog sites to study the geology and mineralogy of Mars [2].

We carry out geological and mineralogical mapping of the Altiplano-Puna volcanic complex and its vicinity using Hyperion hyperspectral imager onboard the Earth Observing One (EO-1) satellite. This is done in order to accomplish three goals: 1) Understand the regional context of the samples collected from this area in previous field expeditions; 2) Improve interpretations of similar datasets of Mars; and 3) Utilize the advantage of remote sensing to better understand the geology and mineralogy of Altiplano-Puna volcanic province. In this work, we present our first attempts at characterizing potential feldspar spectral signatures to give insights into recent feldspar detections on Mars [3].

2. EO-1 Hyperion

EO-1 Hyperion is NASA's spaceborne hyperspectral imaging instrument that operated from 2000 to 2017. It contained 220 spectral bands in the 0.4 to 2.5 µm wavelength range. Two separate detectors, visible-near infrared (VNIR) and shortwave infrared (SWIR) detectors, operated in the 0.4–1.0 µm and 0.9–2.5 µm ranges, respectively, with 30 m/pixel spatial resolution.  Hyperion acquired data in push-broom method, and its products are usually long, narrow strips of hyperspectral cube with 7.7 km swath width.

3. Methods

Hyperion L1T GeoTiff radiance products were downloaded from US Geological Survey Earth Explorer data portal and converted to reflectance using ENVI FLAASH atmospheric correction tool. Reflectance image cubes, which contained noticeable amounts of noise and occasional unrealistically large/small values, were first despiked and then smoothed with a sliding median method using a custom made program for processing spectral data known as Mineral Recognizer [3].

Using the processed data, we computed band depth index at 1.3 µm (BD1300) in a similar manner as those done for Mars hyperspectral data [4] in order to infer the presence of feldspar. As Hyperion spectral bands are not exactly the same as those in Mars hyperspectral data, i.e., Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), we have used slightly different, but overall consistent, wavelengths in computing band depth indices.

In parallel, spectra of samples of ignimbrites, domes, and lava flows collected during previous field campaigns were measured in the laboratory using a portable point spectrometer. The Fieldspec 4 allowed measurements of reflectance spectra from 0.35 to 2.5 µm with three detectors and a minimum spectral resolution of 3 to 8 nm. Finally, the BD1300 spectral index was also computed for collected sample spectra.

4. Results

Identified pixels (BD1300 > 0) (Figure 1) generally corresponded with volcanic domes and pyroclastic flow deposits based on a comparison with a geological map of the Altiplano-Puna volcanic complex [5] and a subset of available samples collected during field campaigns. Band depth indices of identified pixels (0.016-0.039 interquartile range) were generally consistent with those from select samples of volcanic domes and ignimbrites (0.02-0.06). Microscope observation of samples of volcanic domes and ignimbrites indicated that they can contain 0.1–1 mm sized plagioclase feldspar grains in roughly 20-40% abundance. Band depths of the weathered surfaces of the samples were considerably shallower. Likely for this reason, identified pixels were spatially sparse with overall lower magnitudes of 1.3 µm band depth index than those of the samples, indicating detections mainly on relatively fresh surfaces.

5. Summary and Conclusions

Using Hyperion hyperspectral imagery, we computed 1.3 µm band depth index in the Altiplano-Puna volcanic complex. This index is usually known to capture feldspar signatures, although other minerals could induce positive values (e.g. olivine, glass, micas). These minerals are not necessarily present in the analyzed samples, but further work is needed to exclude them from the candidate mineral list. Both volcanic domes and pyroclastic flow deposits with potentially less than 50% plagioclase feldspar abundance were highlighted with the BD1300 index. Our next step is to refine the index computation to more precisely capture the feldspar spectral signature and measure more spectra of samples. Dataset and the processing procedure used in this study are analogous to those for Mars, and our work will likely be useful for solving problems existing in Mars geology, e.g., detection of feldspathic and felsic rocks and interpretation of feldspar spectral signatures using CRISM [2].

Acknowledgements

This work was funded by CNRS Momentum and LUE future leader programs.

References

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[2] Flahaut, J., Martinot, M., Bishop, J. L., Davies, G. R. and Potts, N. J.: Remote sensing and in situ mineralogic survey of the Chilean salars: An analog to Mars evaporate deposits? Icarus, Vol. 282, pp. 152-173, 2017.

[3] Flahaut, J., Barthez, M., Payet, V., Fueten, F., Guitreau, M., Ito, G., Allemand, P., Quantin-Nataf, C.: Identification and characterization of new feldspar-bearing rocks in the walls of Valles Marineris, Mars, European Geophysical Union General Assembly, 4–8 May 2020, Online, 2020.

[4] Viviano-Beck, C. E., Seelos, F. P., Murchie, S. L., Kahn, E. G., Seelos, K. D., Taylor, H. W., Taylor, K., Ehlmann, B. L., Wiseman, S. M., Mustard, J. F. and Morgan M. F.: Revised CRISM spectral parameters and summary products based on the currently detected mineral diversity on Mars. Journal of Geophysical Research: Planets, Vol. 119, pp. 1403-1431, 2014.

[5] Sélles, M. D. and Gardeweg, M. P.: Geología del Área Ascotán-Cerro Inacaliri Región de Antofagasta, Carta Geológica de Chile, Serie Geología Básica, No 190, 2017.