ENHANCEMENT OF ASTROBIOLOGICAL DETECTION POTENTIAL BY FRACTURE-SOURCED FLUIDS NEAR MARS’ DICHOTOMY BOUNDARY

Dispersed exposures of hydrated-minerals within Noachian sediments across Mars’ southern highlands suggest that large areas of the early surface formed under climatic conditions favorable to life [1]. The absence of such sediments from later strata suggests that, after the Early Hesperian, life could only have existed at greater depths [2]. However, detection of astrobiological evidence from either of these periods is made challenging by later burial of Noachian sediments and the inaccessibility of the deep subsurface.

The hydrological evolution of Margaritifer Terra, at the boundary between the highlands and lowlands, created conditions that enhanced the potential for biosignature detection from both periods. This region had a long history of surface water flow [3] and the potential for groundwater upwelling [4]. This activity resulted in the formation of smectite-bearing sediments in low-energy environments, potentially favorable to life [5]. After abundant surface water waned, these sedimentary units were extensively modified by the formation of widespread extensional fractures, most probably in response to the pressurization and/or melting of the resulting cryosphere by intrusive magmatism associated with Tharsis volcanism [6].

Through geomorphological mapping and spectral analysis, we show that fluids emitted by these fractures accomplished significant erosion, removing overburden to reveal Noachian hydrated sediments. We also find evidence for cementation and deposition at the margins of fractures, apparently emplaced by the upwelling fluid. In some regions, this fluid flow is contemporaneous with emplacement of volcanic material from the same fractures, while in others it is not, suggesting that the fluid may have emerged at different temperatures in different regions. Thus, the action of these fluids not only exposed widespread potentially biosignature-bearing Noachian sediments; they may also have deposited evidence for any late-stage deep biosphere.

[1] Mustard, J.F. et al. (2008) Nature, 454, 305-309. [2] Michalski, J. (2013) Nat. GeoSci. 6:2, 133-138. [3] Grant, J. & Parker, T. (2002) JGR, 107:E9, 5066. [4] Andrews-Hanna, J. et al. (2010) JGR: Planets 115:6. [5] Salvatore, M. et al. (2016) JGR: Planets, 121:3. [6] Chapman, M. & Tanaka, K. (2002) Icarus, 155:2, 324-339.