2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 111-11
Presentation Time: 10:55 AM

ACID-SULFATE FUMAROLE ALTERATION AND NEAR-NEUTRAL SINTER PRECIPITATION AT LASSEN: POTENTIAL ANALOG FOR GUSEV CRATER, MARS


MCHENRY, Lindsay J.1, GERARD, Teri L.2 and CARSON, George L.2, (1)Department of Geosciences, University of Wisconsin- Milwaukee, 3209 N Maryland Ave, Milwaukee, WI 53211, (2)Geosciences, University of Wisconsin- Milwaukee, 3209 N Maryland Ave, Milwaukee, WI 53211

Hydrothermal alteration has been invoked for the formation of silica-rich and sulfate-rich deposits near Home Plate at Gusev Crater, Mars. Ruff et al. (2011) suggest a near-neutral sinter precipitating hot spring environment for the silica-rich deposit, while others have inferred acid-sulfate fumarole related leaching. Distinguishing between these two possibilities is important, since a near-neutral system would be more habitable. Terrestrial fumarole and hot spring environments can help constrain the conditions of potential Martian hydrothermalism.

Lassen volcano in the southern Cascades has varied hydrothermal environments, including both acid-sulfate fumarole (Sulphur Works, Bumpass Hell) and near-neutral sinter depositing hot springs (Growler and Morgan). Lassen has a two-phase hydrothermal system, where boiling at depth concentrates sulfuric acid in a vapor phase that emerges as acid-sulfate fumaroles at higher elevations, while the remaining neutral thermal waters emerge at lower elevation hot springs.

Our analyses of water, mineral, and substrate samples document varied hydrothermal environments at Lassen. pH for surface hydrothermal waters ranged from 1.88 (Boiling Springs Lake) to 8.09 (Growler Hot Spring), with most between 2 and 4. Conditions also varied from oxidizing (Sulphur Works fumaroles) to reducing (Growler Hot Spring). Devil’s Kitchen showed the widest range of conditions, with varied oxidation potentials and a pH range of 2.07 (oxidizing) to 5.92 (reducing) within meters. Alteration products are dominated by sulfates (mostly Al and Fe), silica phases (quartz, tridymite, cristobalite, amorphous), and clays (kaolinite, smectite) but also include sulfides (pyrite, marcasite) depending on the environment. Silica-rich deposits formed by varied mechanisms: leaching by acid-sulfate fumaroles and sinter precipitation from near-neutral hot springs. TiO2 concentrations are elevated in the leached deposits and depleted in the sinters, and accessory minerals also differ.

Lassen is an example of a single hydrothermal system that produces both acid-sulfate fumarolic leached deposits (and associated sulfate minerals) and near-neutral sinter precipitates in close proximity. This is a potential analog for the diverse hydrothermal deposits observed by near Home Plate on Mars.

Session No. 111

T224. When Water Meets Rock: Aqueous Alteration in the Solar System I
Monday, 20 October 2014: 8:00 AM-12:00 PM
301 (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.286
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