Hydrothermal Alteration at Devil's Kitchen in the Lassen Volcanic National Park: a Mars Analogue

Abstract

The Devil’s Kitchen hydrothermal site, within the Lassen Volcanic National Park, has hydrothermal features that cover a wide range of pH conditions (2-7). Analysis of mineral precipitates, hot spring mud, unaltered substrate rock, and hot spring and meteoric water reveal a wide variety of alteration minerals, geochemical conditions, and water chemistry. Mineral suites included primary igneous phases, silica phases, clay minerals, and sulfate phases. Aluminum sulfates are the dominant sulfate species present with abundant Na+, Fe3+, and Ca2+ sulfate phases and less common K+ sulfates. Amorphous silica precipitates were observed in three samples from a near-neutral hot spring and one from an acidic hot spring. When compared to the unaltered substrate, hydrothermal mud samples from acidic and near-neutral hot springs are depleted in more mobile cations (Mg, Ca, Na, and Mn) and enriched in immobile elements like TiO2 which is consistent with acid-sulfate hydrothermal alteration with a high water-rock ratio. Altered sediments show more geochemical variation between acidic and near-neutral conditions than the mud samples. Altered sediments from acidic hot springs show variable enrichment and depletion in silica and titanium while precipitate samples from near-neutral hot springs are more enriched in aluminum and silica. Water analysis shows that high sulfate concentrations correlate with low pH waters. The hot spring waters also have a high concentration of mobile cations (Mg+, Na+, and Ca2+) which is consistent with the waters dissolving minerals from the dacitic substrate. This wide range of hydrothermal conditions present in a small area makes Devil’s Kitchen a good terrestrial analogue for the proposed hydrothermal system at the Home Plate site on Mars. Both acid-sulfate leaching and near-neutral silica-sinter producing hot springs have been proposed to explain the deposits found near Home Plate. The Devil’s Kitchen hydrothermal system could represent a terrestrial analogue where both acid-sulfate leaching and near-neutral silica-sinter deposition occur within the same system near each other.