77-6 Ancient Fracture (Boxwork?) Patterns at Jezero Crater, Mars: Possible Expressions of Post-Impact Fluid Flow

Session: Boxwork and Fracture Halos: Changes in mineralogy and erosion resistance around fracture features on Earth, Mars, and across the Solar System

Presenting Author:

Alicia Vaughan

Authors:

Vaughan, Alicia¹, Ravanis, Eleni², Bedford, Candice C.³, Broz, Adrian⁴, Johnson, Jeffrey Roy⁵, Wiens, Roger C.⁶, Bell, James F.⁷

(1) Space Science Institute, Flagstaff, AZ, USA, (2) University of Hawai?i at Manoa, Honolulu, HI, , (3) Purdue University, West Lafayette, IN, USA, (4) Purdue University, West Lafayette, IN, USA, (5) Johns Hopkins University, Laurel, MD, , (6) Purdue University, West Lafayette, IN, USA, (7) Arizona State University, Tempe, AZ, ,

Abstract:

The Perseverance rover has observed boxwork-like fractured bedrock in two locations (Oslobreen and Le Meix) along its traverse of the outer Jezero crater rim, both thought to be Noachian in age.  These features might have been associated with hydrothermal or groundwater systems resulting from the impact that formed Jezero crater, so are important targets for studying geologic context and astrobiologic potential for early Mars. These relatively small exposures are characterized by intersections of ~0.5 to 1 m-wide bedrock ridges creating boxwork-like patterns that are identified and separated by recessed areas filled with regolith. The patterns were initially observed in orbital HiRISE images and are visible in surface images from Mastcam-Z. In both locations, Mastcam-Z multispectral data show that the fractured, ridge-forming rocks contain low-calcium pyroxene (LCP). Additional SuperCam visible-infrared (VISIR) spectroscopic data at Le Meix show evidence of LCP and hydrated sulfates. These ridges are also associated with rubbly, cobble-to pebble-sized, Fe-poor rock fragments situated within their interior that appear to be locally derived. Based on Mastcam-Z observations with supporting instrument data in other locations of the Jezero rim, this Fe-poor material could be consistent with either a high-Si phase or feldspar. Chemical data acquired by SuperCam LIBS within the Le Meix area show elevated chemical indices of alteration (CIA) indicative of open-system alteration. At an area 300 m away, SuperCam acquired VISIR data on a fracture-associated halo feature that showed an Al-phyllosilicate signature (~2.21 micron band) and high CIA values, which indicates that bedrock fractures likely acted as conduits for fluid flow generally in the region. Given the Noachian age and geologic setting, one plausible formation mechanism for these patterns and corresponding mineralogical signatures is impact- or volcanic-induced hydrothermalism, whereby warm fluids flow through a fracture system and deposit Fe-poor mineral precipitates. Subsequent aeolian erosion exploits the relative erosional weakness of the surrounding material to leave the observed boxwork-like pattern. Should Perseverance encounter more of these features on its continued exploration, we recommend a dedicated investigation using the entire payload to better understand the small-scale textures and detailed chemistry of both the ridge material and associated Fe-poor fragments. This would help us to further constrain their origin and compare them to other, more prominent boxwork patterns on Mars.

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