Very low-temperature alteration of sideromelane in hyaloclastites and hyalotuffs from Kilauea and Mauna Kea volcanoes: Implications for the mechanism of palagonite formation

Abstract

Three petrographically distinct styles of altered glasses in two hyaloclastites and one hyalotuff were studied. The texture and chemistry of these samples were investigated using electron probe microanalysis, scanning electron microscopy and transmission electron microscopy in order to understand better the mechanism by which alteration of sideromelane and formation of palagonite occurred in these samples. The results show that clay minerals (primarily smectites) are present in three different microenvironments: (1) coating the surfaces of glass and crystals or vesicle walls; (2) as a relatively heterogeneous, but well crystallized, replacement product (i.e. reddened smectite grain replacement or RSGR) of glass or; (3) as a relatively homogeneous, amorphous to poorly crystalline replacement product (i.e. palagonite). Both the grain size and composition of these smectite-like materials vary considerably.Crystalline smectites occur in both hyaloclastites and have an intermediate composition between the two end-members nontronite and saponite. This composition could correspond to a mechanical intergrowth and/or an interstratification of two different smectites: one dioctahedral (i.e. nontronite) and one trioctahedral (i.e. saponite or stevensite) or simply to a true di-trioctahedral smectite. The coating smectite appears to have precipitated by a paragenetically-early, dissolution-precipitation mechanism prior to the formation of the RSGR. The high Ti content found in RSGR is attributable to an amorphous Ti-rich material which is intergrown with smectite and which behaves as a sink for immobile elements and those not included in smectite.Palagonite from both hyaloclastites and hyalotuff is poorly to non-crystalline and more aluminous than the coating smectites. Palagonite from the hyalotuff has an Fe-rich montmorillonite-like composition. The TEM images show a 30–50 nm thick leached layer formed by selective (non-stoichiometric) dissolution that takes place in the fracture domain. The hydration and replacement of glass during the palgonitization process is accompanied by the loss of Fe, Mg and Ca with a concomitant gain of Al. Both palagonites (from hyaloclastites and hyalotuff) show smilar textural and chemical characteristics.

Evidence of volcanic and glacial activity in Chryse and Acidalia Planitiae, Mars

“…Most terrestrial hyaloclastites are basaltic in composition and are a mixture of crystalline fragments and sideromelane (basaltic glass), an unstable material that in a low-temperature, aqueous environment undergoes palagonitic alteration. Palagonitization produces smectites (Hay and Iijima, 1968;Singer, 1974;Jakobsson, 1978;Eggleton and Keller, 1982;Jakobsson and Moore, 1986;Zhou et al, 1992;Bishop et al, 2002) ranging in composition between Mg-rich and Fe-rich endmembers (Drief and Schiffman, 2004). Since glass has very subtle spectral features, the spectroscopic signature of hyaloclastic deposits is dominated by that of Mg-and Fe-rich smectites.…”

A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology

“…An alteration mechanism similar to palagonitization. The palagonitization of volcanic glass is another alteration process that is known to form conspicuous microtextures, which in some cases exhibit spheroidal or elliptical structures (Thorseth et al, 1991;Stroncik and Schmincke, 2002;Drief and Schiffman, 2004;Cockell et al, 2009) that are morphologically relevant to evaluating the origin of the ovoid structure described here, especially when the palagonite grows as concentrically banded rinds around vesicle walls (e.g., see Figs. 11 and 14 in Walton and Schiffman, 2003;Fig.…”

Science Applications of a Multispectral Microscopic Imager for the Astrobiological Exploration of Mars

“…It has been defined in various ways in the literature with differing compositions and textures (Peacock, 1926;Moore, 1966;Thorseth et al, 1991). Depending on the stage of alteration, its composition varies from hydrated Fe oxides in the early stages of alteration (typical of lower-temperature weathering) (Thorseth et al, 1991;Bishop et al, 2002c;Drief and Schiffman, 2004;Pokrovsky et al, 2005) to Fe, Mg-rich clay minerals, zeolites, and hydrated silica for more advanced alteration at elevated temperature (Griffith and Shock, 1995;Bishop et al, 2002c;Warner and Farmer, 2010).…”