Mineralogy of cones in the western part of Isidis Planitia

Many cones on Isidis Planitia form subparallel chains several kilometers in length. This region have characteristic pattern of cones or cone chains- called a “fingerprint” [1]. Our analysis of chains of cones indicates that they can be grouped in larger systems. We considered one of these systems in the northwestern part of Isidis (central location: 14.235°N; 83.096°E).

We selected one standout spectrum that comes from the CRISM FRT00009260 scene but is typical for the entire image area. The scene just comes from the northwestern part of Isidis, where the characteristic chains of cones are visible. The types of cones from our division [2], belong to the group of chains of separate cones and without a furrow. The spectrum shows the minima 1.49; 1.98; 2.04 µm which we assigned to individual minerals. Additionally, the ~ 2 µm range is disturbed by Martian CO₂ influences, which is caused by the imperfect separation of the atmosphere by the “volcano - scan algorithm” (by the atmosphere above Olympus Mons). Gypsum appears to be the most suitable mineral for these minima, although alunites can also be considered. The clay minerals widespread on Mars do not resemble in the observed minima. From the generated endmembers, it can be seen that minerals are accumulated around the cones.

Gypsum is a mineral formed in the process of evaporation and crystallizes from salty, drying water reservoirs. Because Isidis might once have been a highly saline reservoir, gypsum crystallization could occur under such conditions, especially in depressions. Alunites, on the other hand, are products of volcanic exhalation, which would explain the origin of the cones. Common alunites have been found on the La Fossa Crater Volcano, Aeolian Islands [3] as volcanic exhalations and in the vicinity of Las Vegas, Nevada, where alunites with gypsum were mapped based on aerial photos [4]. On Mars in the northeast of Hellas Basin, gypsum and ammonioalunites were interpreted on the basis of the PFS and OMEGA (MEX) spectra [5], [6]

These are our preliminary comparisons that still require further evaluation. The next stage of the work will be to explain the mechanism of the formation of these forms, based on known geological phenomena but in relation to Mars. We want to clarify whether the designated areas were created in the same geological processes, or whether a different mechanism is responsible for the differences in these forms. We take the phenomenon into account that instability of water in the upper layers of the regolith could cause rapid degassing of the regolith [7].

References: [1] Guidat, T. et al. (2015) Earth and Planet. Sci. Let . 411, 253-267. [2] Zalewska N. et al. (2021) LPS 52nd, Abstract # 2710. [3] Parafiniuk J. (2012) Bulletin of the Polish Geolog. Instit. 452, 225-236. [4] Kirkland E. et al. (2007) LPS XXXVIII, Abstract # 2232. [5] Zalewska N. (2013) Planet. Space Sci. 78, 25-32. [6] Zalewska N. (2014) GeoPl. Earth and Planet. Sci. 65-76. [7] Czechowski L. et al. (2021) LPS 52nd, Abstract # 2740.