51st Lunar and Planetary Science Conference (2020) 1713.pdf

ALTERED VOLCANIC MATERIAL FROM FUERTEVENTURA, SPAIN AS A POSSIBLE ANALOGUE FOR THE MARTIAN SURFACE. Z. F. M. Burton1,2, J. L. Bishop2, and J. M. Danielsen3, 1Stanford University (Stanford, CA; [email protected]), 2The SETI Institute (Mountain View, CA), and 3San Jose State University (San Jose, CA).

Introduction: Volcanism has been a persistent and Study Site: Altered ash and tephra samples were important process operating throughout much of mar- collected in 2015 from numerous locations at the Gairía tian history [1]. The martian surface is characterized by Caldera of Fuerteventura (Fig. 1), including along the the predominance of mafic and ultramafic material, rim of the caldera (Fig. 2). The Gairía Caldera is located while volcanic landforms including cinder cones, in a volcanically young (inferred Holocene age) land- shields, domes, and volcanic plains typify morphologi- scape characterized by a generally basaltic composition cal features on Mars [1]. Importantly, aqueous alteration and including features such as cinder cones, craters, and of mafic and ultramafic material (especially basalt) is lava fields [8]. interpreted to be largely responsible for the suite of Methods: Ash and tephra samples (e.g. Fig. 3) were phyllosilicates and sulfates observed on Mars [2-5]. dry sieved (sample names ending in “a”) or ground from Therefore, understanding of the nature of altered vol- coarse material and dry sieved (sample names ending in canic martian regolith is critical to understanding of sur- “b” or “d”) to obtain <125 µm size fractions [9]. Spectra face weathering, geochemical alteration, and the for- of these samples were collected both via visible/near- mation of the observed suite of aqueous minerals on and infrared (VNIR) reflectance spectroscopy measured near the surface of Mars. Fortunately, terrestrial ana- from 0.35-2.5 µm under ambient conditions using an logues provide the opportunity to study products of ge- ASD spectrometer at the SETI Institute, as described in ological and climatic processes akin to those that have [9], and via bidirectional reflectance spectroscopy existed on Mars [e.g. 6]. Here, we characterize Holo- measured from 0.3-2.55 µm and FTIR reflectance spec- cene surface and near-surface ash and tephra collected troscopy from 1-25 µm under dry conditions using the from near the Gairía Caldera on the volcanic island of RELAB facility at Brown University, as described in Fuerteventura (Canary Islands, Spain) (Fig. 1) as poten- [10]. Here, we focus on the spectra from ~0.3 to 4 µm. tial analogues for altered volcanic material on Mars. The volcanic origin, aqueous alteration, minimal precipita- tion, powerful winds, and sparse or absent vegetation found on Fuerteventura make the region a potentially compelling Mars analogue site [7,8].

Figure 2. View of the rim of Gairía Caldera.

Figure 1. Satellite image of Fuerteventura with inset map of island’s geographic location (red pin). Study site location at Gairía Caldera indicated by red circle. Figure 3. Example of tephra collected at caldera rim. 51st Lunar and Planetary Science Conference (2020) 1713.pdf

Figure 4. Reflectance spectra of dry sieved samples Figure 5. Reflectance spectra of ground and sieved from selected locations. Lines mark spectral features. samples from Fig. 4. Lines mark spectral features.

Results: We investigated the spectral properties of consistent with more finer grains due to grinding, but several altered volcanic samples: JB1552 (surficial light show no changes in mineralogy. brown ash/tephra and underlying sand), JB1553 (surfi- Summary and Implications for Mars: Spectros- cial darker brown/black ash/tephra and underlying copy of volcanic material from Gairía Caldera on the is- sand), JB1554 (surficial black tephra), JB1555 (black land of Fuerteventura indicates the ubiquity of mafic fines/tephra ~5 cm beneath JB1554), JB1556 (brown material, as expected, but also reveals the presence of sand-sized material underlying black tephra near aqueous alteration products such as phyllosilicates in JB1554), and JB1557 (orange soil/loose material). As the lighter-colored material characterized here, but not expected, spectra of the lighter, soil materials (JB1552, in the darker-colored, less altered material. Due to the JB1553, JB1557) have overall higher reflectances and geological and climatic setting – as well as the chemical stronger bands attributed to phyllosilicates (Figs. 4 & 5). composition – of these materials, the Gairía Caldera site Water bands near 1.41 and 1.91 μm and Al-OH bands may therefore represent a compelling analogue for mar- near 2.21 and 2.76 µm are characteristic of montmoril- tian regolith in both its altered and unaltered form. This lonite [10]. The stronger phyllosilicate bands in these is especially relevant for understanding the conditions samples indicate a higher degree of aqueous alteration. by which the suite of aqeuous minerals observed at the A band near 1 μm indicates Fe2+ in all samples, likely martian surface may have formed. due to basaltic glass or pyroxene. The ~3 µm band is References: [1] Greeley & Spudis (1981) Rev. Geophys., much broader in the darker samples, consistent with vol- 19, 13-41. [2] Bibring et al. (2005) Science, 307, 1576-1581. [3] Gendrin et al. (2005) Science, 307, 1587-1591. [4] Lange- canic glass. Weak features due to carbonates are ob- vin et al. (2005) Science, 307, 1584-1586. [5] Poulet et al. served near 4 µm in spectra of samples JB1552a, (2005) Nature, 438, 623-627. [6] Gibson et al. (1983) JGR, JB1555a, and JB1553d. Comparison of the sieved (Fig. 88, A912-A928. [7] Schmincke (1976) The geology of the Ca- 4) and ground (Fig. 5) samples reveals darkening of the nary Islands. [8] Dóniz-Páez (2009) Nimbus, 23-24, 89-103. three soil samples and weaker clay bands, indicating the [9] Danielsen et al. (2017) LPSC, Abs. #2773. [10] Bishop et al. (2008) Clay Miner., 43, 35-54. sieved soils contain a larger abundance of fines that con- Acknowledgements: We thank the NASA Astrobiology centrated the clay fraction. Ground versions of JB1552 Institute (NAI #NNX15BB01), the Clay Minerals Society and JB1557 have greater reductions in the clay fraction (Student Research Grant), and the Geological Society of than sample JB1553. In contrast, the ground versions of America (Graduate Student Research Grant) for financial sup- the three glassy tephra samples are slightly brighter, port. We thank T. Hiroi (Brown University) for RELAB work.