Habitability of Hydrothermal Systems at Jezero and Gusev Craters as Constrained by Hydrothermal Alteration of a Terrestrial Mafic Dike

Abstract

NASA's search for habitable environments has focused on alteration mineralogy of the Martian crust and the formation of hydrous minerals, because they reveal information about the fluid and environmental conditions from which they precipitated. Extensive work has focused on the formation of alteration minerals at low temperatures, with limited work investigating metamorphic or high-temperature alteration. We have investigated such a site as an analog for Mars: a mafic dike on the Colorado Plateau that was hydrothermally altered from contact with groundwater as it was emplaced in the porous and permeable Jurassic Entrada sandstone. Our results show evidence for fluid mobility removing Si and K but adding S, Fe, Ca, and possibly Mg to the system as alteration progresses. Mineralogically, all samples contain calcite, hematite, and kaolinite; with most samples containing minor anatase, barite, halite, and dolomite. The number of alteration minerals increase with alteration. The hydrothermal system that formed during interaction of the magma (heat source) and groundwater would have been a habitable environment once the system cooled below ~120° C. The mineral assemblage is similar to alteration minerals seen within the Martian crust from orbit, including those at Gusev and Jezero Craters. Therefore, based on our findings, and extrapolating them to the Martian crust, these sites may represent habitable environments which would call for further exploration and sample return of such hydrothermally altered igneous materials.

Keywords: Gusev Crater; Hydrothermal; Jezero Crater; Mars Alteration; NE Syrtis; Terrestrial Analog.

Figure 1.

Field site showing each of the four visually distinct alteration zones of the dike. The alteration and oxidation of the dike changes from the ‘darkest’ zone (a), the ‘green’ zone (b), the ‘purple’ zone (c), and the ‘red’ zone (d). The dike exhibits increasing oxidation from zone a through d. Hammer and chisel for scale.

Figure 2.

Hand samples with fresh cut surfaces of different regions of the dike: a) dark, b) green, c) purple, and d) red. All samples show some alteration but with increasing oxidation/alteration going from A to D.

Figure 3.

Bulk rock chemistry from each zone normalized to the ‘darkest’ zone of the dike. Values less than one indicate elements that have been depleted compared with the least altered sample and therefore were removed from the system during alteration, while values greater than one indicate elements that are enriched compared to the darkest sample and are therefore added to the bulk chemistry of the system during alteration.

Figure 4.

Stacked VNIR reflectance spectroscopy data from each of the four zones of the dike. Moving from top to bottom, these zones include the ‘darkest’ zone (a), the ‘green’ zone (b), the ‘purple’ zone (c), and the ‘red’ zone (d). Shape of the minima show alteration minerals.

Figure 5.

The fluid history of the dike/water interaction during/after dike emplacement within the sandstone. Note that this figure focuses on the reactions in the dike. (A) Intrusion of the dike into the sandstone producing a hydrothermal system circulating through the sandstone and penetrating the dike after cooling below its ductile temperature and fracture formation; (B) shows the system as the dike and fluids cool. Green arrows indicate element mobility. Red arrows represent hot fluids, while blue arrows represent cold fluids. Orange sub-box shows the alteration minerals forming within the dike: yellow squares represent phlogopite, white laths represent feldspar altering to kaolinite, brown rhombohedra represent olivine casts, light blue represents calcite, and black lines represent oxide minerals; (C) shows the dike system after erosion and how it appears today – colors correspond to coloration of the dike shown in Figure 1.