Mineral‐Filled Fractures as Indicators of Multigenerational Fluid Flow in the Pahrump Hills Member of the Murray Formation, Gale Crater, Mars

Abstract

Mineral‐filled fractures (veins) are valuable indicators of deformation and fluid flow within a sedimentary package. Information obtained from vein morphology, texture, and chemistry may elucidate the sequence and nature of postdepositional fluid events. Additional information from vein patterns and interactions between veins and host rock provides insight into fracture formation mechanism(s). The widespread occurrence of veins and other diagenetic features in the sedimentary rock record preserved in Gale crater, Mars, indicates that postdepositional fluids were regionally active considerably later in time than the primary fluviolacustrine environments responsible for the deposition of Mount Sharp strata. Here we report a suite of veins within the Murray formation at the Pahrump Hills locality that were investigated using the scientific payload of the Mars Science Laboratory Curiosity rover. Based on an analysis of vein color, morphology, and texture, and corroborated by vein chemistry, we interpret three distinct vein types at Pahrump Hills: gray veins, white veins, and dark‐toned veins. These veins represent distinct, separate episodes of postdepositional fluid flow, suggesting a protracted history of fluid stability in Gale crater. Additionally, we utilize vein patterns across multiple lithologies at the Pahrump Hills field site to suggest hydrofracture as the primary mechanism of fracture formation.

Extensive Polygonal Fracture Network in Siccar Point group Strata: Fracture Mechanisms and Implications for Fluid Circulation in Gale Crater, Mars

“…Polygon boundaries are light‐toned relative to surrounding host rock. Although lighter tone in images might, in part, reflect illumination on topographic highs, we suggest that the topographic relief supports the potential for either a secondary mineral phase within fractures or fluid modification of bedrock adjacent to the fracture, as has been observed by the Curiosity rover (Kronyak et al, ; Nachon et al, , ; Yen et al, ).…”

“…The Stimson formation contains abundant evidence for postdepositional fluid flow along discrete fractures. Most prominently, calcium sulfate‐filled hydrofracture veins occur in both the Stimson formation and underlying Murray formation (Kronyak et al, ). Veins in the Stimson formation, however, are generally thinner and scarcer than those observed in the underlying Murray formation, and, in several locations, do not appear to cross the contact with the Stimson formation.…”

“…Calcium sulfate veins are present within Mount Sharp and SPg strata, and many exhibit enhanced relief (cf. Kronyak et al, ; Nachon et al, ), yet there is no evidence that mineral veins are directly associated with polygons. Similarly, although alteration haloes are occasionally associated with polygons, this relationship is not uniquely linked to observed polygons.…”

“…Several distinct fracture systems occur in Gale crater, Mars, within the field area of the Mars Science Laboratory Curiosity rover. Images from the Curiosity rover record a variety of fracture morphologies, mineral veins, and fracture‐associated alteration halos (Frydenvang et al, ; Kronyak et al, ; Nachon et al, , ; Yen et al, ). The majority of these features have been broadly attributed to hydrofracturing (Caswell & Milliken, ; Kronyak et al, ) during postdepositional fluid flow and are interpreted to reflect circulation of deep subsurface groundwater through the sediment package during burial.…”

“…Images from the Curiosity rover record a variety of fracture morphologies, mineral veins, and fracture‐associated alteration halos (Frydenvang et al, ; Kronyak et al, ; Nachon et al, , ; Yen et al, ). The majority of these features have been broadly attributed to hydrofracturing (Caswell & Milliken, ; Kronyak et al, ) during postdepositional fluid flow and are interpreted to reflect circulation of deep subsurface groundwater through the sediment package during burial. Polygonal fractures have also been described from elsewhere in Gale crater, including centimeter‐scale features attributed to desiccation of surficial fluids (Stein et al, ) and decameter‐scale polygons attributed to noncyclic desiccation or thermal contraction events (i.e., boxwork structures; Siebach & Grotzinger, ).…”