Solfataric Alteration at Hawaii as a Potential Analog for Martian Surface Processes

Abstract:

Hydrothermal and/or acidic alteration of basaltic ash on Mars may have produced the sulfates and hydrated silica observed in many aqueous outcrops. This study considers solfataric alteration as a potential formation mechanism for opal, sulfate and clays on Mars. Alteration via fumaroles in the Kilauea caldera, HI, have created a light-toned solfataric bank on the south wall of the crater where Keanakakoi ash was deposited. Bands of orange, beige and whitish crusted material are present where jarosite and gypsum are observed in a silica/clay matrix. We have analyzed the chemistry and mineralogy of several chunks and particulate samples from this site using visible/near-IR (VNIR), mid-IR and Mössbauer spectroscopies as well as XRD, SEM and BSE imaging.

Mineralogical analyses show the presence of opal, saponite, gypsum, jarosite and ferric oxides/hydroxides in the ash as well as remnants of the original basaltic components and volcanic glass. The alternating bands of light-toned gypsum-bearing material and orange-colored bands of jarosite-bearing material likely mark changes in the acidity of the hydrothermal fumes. SEM reveals Fe sulfate, Mg smectite and palagonitic rinds surrounding sideromelane and pyroxene crystals. Mössbauer spectra indicate the presence of ferric oxide-bearing species in addition to jarosite. The VNIR spectra show changes in the Fe bands for the bright and orange bands in the outcrop. The VNIR spectra also include features consistent with hydrated silica, gypsum, jarosite and saponite. XRD shows that opal-A is prevalent over opal-CT. Mid-IR reflectance and emissivity spectra are consistent with gypsum, jarosite, and silica. Bulk chemical analyses and BSE imaging indicate basaltic components in addition to the opal, sulfates and saponite. Using multiple lab techniques to characterize the alteration products of hydrothermal and solfataric alteration on Kilauea, we hope to enable improved interpretation of orbital and in situ data of Mars.