The surface of Mars exhibits strong evidence for a widespread and long-lived cryosphere. Observations of the surface have identified phases produced by water-rock interactions, but the contribution of glaciers to the observed alteration mineralogy is unclear. To characterize the chemical alteration expected on an icy early Mars, we collected water and rock samples from terrestrial glaciated volcanics. We related geochemical measurements of meltwater to the mineralogy and chemistry of proglacial rock coatings. In these terrains, water is dominated by dissolved silica relative to other dissolved cations, particularly at mafic sites. Rock coatings associated with glacial striations on mafic boulders include a silica-rich component, indicating that silica precipitation is occurring in the subglacial environment. We propose that glacial alteration of volcanic bedrock is dominated by a combination of high rates of silica dissolution and precipitation of opaline silica. On Mars, cryosphere-driven chemical weathering could be the origin of observed silica-enriched phases.
Bibliographical noteFunding Information:
We gratefully acknowledge the Solar Systems Workings (SSW) program (Grant NNX16AG38G). We thank the National Forest Service for granting us access to the sample locations. We thank all those who assisted with fieldwork, as well as Phil Christensen, Everett Shock, and Gwyneth Gordon at ASU. We thank Marty Frisbee at Purdue University and Eve Berger at JSC. We thank the two anonymous reviewers for their helpful comments. The data used to support this paper's conclusions can be found in Data Set S1.
©2018. The Authors.
- glacial alteration
- rock coatings
- silica dissolution