Silica coatings in the Ka'u Desert, Hawaii, a Mars analog terrain: A micromorphological, spectral, chemical, and isotopic study

Abstract

[1] High-silica materials have been observed on Mars, both from orbit by the CRISM spectrometer and in situ by the Spirit rover at Gusev Crater. These observations potentially imply a wet, geologically active Martian surface. To understand silica formation on Mars, it is useful to study analogous terrestrial silica deposits. We studied silica coatings that occur on the 1974 Kilauea flow in the Ka'u Desert, Hawaii. These coatings are typically composed of two layers: a ∼10 mm layer of amorphous silica, capped by a ∼1 mm layer of Fe-Ti oxide. The oxide coating is composed of ∼100 nm spherules, suggesting formation by chemical deposition. Raman spectroscopy indicates altered silica glass as the dominant phase in the silica coating and anatase and rutile as dominant phases in the Fe-Ti coating; jarosite also occurs within the coatings. Oxygen isotopic contents of the coatings were determined by secondary ion mass spectrometry (Cameca 7f and NanoSIMS). The measured values, d18 O Fe-Ti = 14.6 ± 2.1‰, and d 18 O silica = 12.1 ± 2.2‰ (relative to SMOW), are enriched in 18 O relative to the basalt substrate. The observations presented are consistent with a residual formation mechanism for the silica coating. Acid-sulfate solutions leached away divalent and trivalent cations, leaving a silicaenriched layer behind. Micrometer-scale dissolution and reprecipitation may have also occurred within the coatings. Chemical similarities between the Hawaiian samples and the high-silica deposits at Gusev suggest that the Martian deposits are the product of extended periods of similar acid-sulfate leaching.

Glaciovolcanic hydrothermal environments in Iceland and implications for their detection on Mars

“…Indeed, much Mars analogue work has been conducting focusing on a range of environments, including Hawaiian lava flows (e.g. Chemtob et al 2010), acid hot springs (e.g. Szynkiewicz et al 2012); impact craters (e.g.…”

Detection and Mapping of Black Rock Coatings Using Hyperion Images: Sudbury, Ontario, Canada

“…Remote sensing techniques are potentially well suited for discrimination and mapping of exposed black rock coatings, and correspondingly may be helpful in highlighting areas most affected by past or ongoing environmental degradation resulting from smelting activities. The formation mechanisms of black rock coatings are similar to acid-sulfate processes that operate under natural conditions in regions of volcanic and hydrothermal activity [2,[5][6][7], and the application of remote sensing techniques toward the discrimination of smelter-related coatings is thus relevant to the broader topic of the remote detection of acid-sulfate deposits. Problematically, discrimination of smelter-related black rock coatings can prove challenging as a result of the absence of distinctive features in the reflectance spectra of coatings [8].…”

Transport and modification of glaciovolcanic glass from source to sink on Mars

“…In an experimental study of bioalteration of basaltic glass from Surtsey, silicic rinds of ß1 μm thickness developed from microbial leaching of the grain exterior (Thorseth et al, 1995). The physical and chemical characteristics of these rinds are generally comparable to those formed by abiotic leaching (Minetti et al, 2007;Chemtob et al, 2010;Seelos et al, 2010), although it would go too far to tie biotic process to the silicic spectral properties observed on Mars. More importantly, the process of bioalteration illustrates how basaltic glass can act as an accessible substrate for microorganisms due to the bioavailability of nutrients in the glass structure.…”

“…However, the observed effectiveness of aeolian transport in altering PSDs also calls into question the exact origins of the silicic spectral signatures of weathered basaltic glasses on Mars. Observations of rinds with comparable spectral properties of basaltic glasses from Hawaii indicate that acidic leaching commonly produces rinds of several micrometres thick (Minetti et al, 2007;Chemtob et al, 2010;Seelos et al, 2010). If the rate of alteration in the experiments (Fig.…”