Investigating the complex history of a mountain glacier in Argyre Basin, Mars: Potential for warm-based glaciation?

Introduction: Glacier-like forms (GLFs) are a particular class of viscous flow formations (VFFs) that occupies the mid-latitudes of Mars [e.g., 1–4]. They appear to be concentrated around the 40–55 latitude range in both hemispheres [3,4]. Their distribution signifies changes in water-ice latitudinal stability with obliquity variations. Therefore, studying them and understanding their evolution is critical to understanding the recent glacial history of Mars and stability of ice on its surface. For this study, we focus one a GLF in Argyre (Fig. 1). In earlier updates (e.g., [5]), we showed that the glacier system displays 1) multi piedmont-like terminal lobes, 2) gullied cirque-like source regions, and 3) periglacial modification of surface materials indicative of near-surface ice. Here, we provide further updates about our mapping, which highlight the complex history of the studied region.

Methods and datasets: We carried out the morphologic investigation using images from HiRISE, CTX and CaSSIS. We created a CTX mosaic for the study region and geo-referenced it to an HRSC DTM to extract morphometric information on flow directions and influence of surrounding topography. Here we describe a number of new observations coupled with morphometric measurements where relevant.

Positive Relief Feature (PRF): The PRF is the main source region for the various VFFs observed around it (Fig. 1). It has an elevation of ~+3250 m and rises ~4250 m above the surrounding terrains to the east, and more than 6000 m above the Argyre floor to the west. It displays a wide mesa-like flat top more than 20 km across along its longest axis with slopes ranging as low as 1° up to 7° in certain areas. The mesa top appears mostly smooth with muted topography in CTX images, suggesting a recently emplaced mantling unit. In contrast, the sides of the PRF are steep (22–32°) with the NE slopes displaying the highest slopes (~32) associated with a semi-circular cirque-like alcove. Based on [6], we interpret this PRF to be an erosional remnant of the basin’s rim materials.

The lobate deposits: The lobate deposits surround the PRF and dominate the terrain from its lower flanks to regions ~10-35 km away, depending on the direction (Fig. 2). They mainly comprise a NE trending lobe, a western deposit that branches into two distinctive lobes trending NW and SW; all three whose flow directions are constrained by surrounding topography resembling Lineated Valley Fills (LVFs) [2], and finally an East-trending unit that flows more feely and displays a Lobate Debris Apron (LDA)-like morphology [2]. All flows display clear terminal ridges and flow fronts, whereas the three LVF types also display sets of quasi-parallel lineations trending along the respective flow direction. The flows show relatively low slopes (typically <5), and show clear signs of viscous deformation as evident from their flow directions around topographic obstacles and surface lineations that develop in response to these movements. The lobate flows appear smooth in CTX and CaSSIS image resolutions with very few fresh-looking impact craters. Certain outcrops that protrude above the surface of the flows display concentrations of fine-grained materials organized in ripple formations. A CaSSIS image covering the western flows acquired in Ls 157 (Southern hemisphere winter) display bright frost accumulations over the same outcrops at preferentially at the west-facing sides (Fig. 3). Notably, we observe a potential paleo drainage feature in the form of quasi-linear valley in close proximity, but not in direct contact with the (current) boundary of the NE lobe (Fig. 4). An inspection of this feature using the HRSC DTM indicates that the valley appears to originate at or beneath a region of brighter fine-grained materials at the lobate boundary, and crucially, traversing over a relatively higher elevation mound, and then extends downslope  ~2 km with a near uniform width of ~150 m (Fig. 5). The area between the mound and the terminal boundary of the lobate deposits also dips in elevation. The valley can be best traced in a CaSSIS image and overall extends up to 2.7 km away from the flow boundary. We plan to better quantify the morphometry using new HiRISE DTMs to verify this stratigraphical relation, and should report about it in more detail at the meeting.

Acknowledgements: MRELM acknowledges funding from the KU internal grant (8474000336-KU-SPSG). G.A.D. is gratefully funded by an UKRI STFC Studentship.

References [1] Arfstrom, J., and Hartmann, W.K., (2005), Icarus, 174, 321–335. [2] Head. J.W. et al. (2010), EPSL, 294, 306–320. [3] Souness, C. et al. (2012). Icarus, 217, 243–255. [4] Hubbard, B. et al. (2014), Cryosphere, 8, 2047–2061. [5] El-Maarry, M.R., Diot, X. (2020), 7th Mars Polar meeting, abstract #2099. [6] Dohm, J.M. et al. (2015), Icarus, 253, 66–98.

Figure 1. [Top] Argyre basin in blended THEMIS Day IR and MOLA with a white box showing the location of the studied landform. [Bottom] 3D view compiled from an HRSC DTM with a CTX mosaic overlaid at 3x vertical exaggeration. A black arrow points to the heavily modified cirque-like accumulation region, and a yellow arrow shows the terminus of the NE lobe.

 

Figure 2. THEMIS Day IR mosaic of the glacial system showing the key landforms described here. White boxes show the locations of Figures 3 and 4.

Figure 3. CaSSIS RGB image acquired during Ls 157 (Southern hemisphere winter) displaying bright deposits, probably CO2 frost, accumulating over fine-grained materials that display ripple features during warmer seasons. (Image ID: MY35_010096_310_0_RGB).

 

Figure 4. CaSSIS image covering the NE lobe and showing the valley feature inclose proximity and appearing to flow away from the NE lobe. Note the dark band circumferential to the current lobe boundary cross-cutting the valley feature as well. (Image ID: MY35_012794_311_0_NPB).

 

Figure 5. CTX mosaic draped over an HRSC DTM showing the valley and the mound it traverses over. Directional lighting has been implemented to highlight the topographical relations.