¹Jiaming Zhu, ¹Bo Wu, ²Zikang Li, ²Yiliang Li
Earth and Planetary Science Letters 680, 119904 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.119904]
¹Planetary Remote Sensing Laboratory, Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
²Department of Earth & Planetary Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong
Copyright Elsevier

The behavior of volatiles is critically important for understanding crustal fluids and the potential existence of a subsurface biosphere on Mars. However, our knowledge of the volatile cycle on Mars is limited by insufficient data from landed rovers and orbiter sensors. Halite salt crusts are widespread in the Qaidam Basin on the northern Tibetan Plateau due to strong evaporation under hyperarid climate conditions. We observed that the halite-dominated salt crust in the desiccated playa area diverts fluids percolating from depth to the surface, leading to the formation of raised polygonal rims enriched in gypsum. We drilled through the salt crust using a hand mill and measured the instantaneous gas concentrations and compositions. Beneath the halite salt crust, significantly higher concentrations of H2O, CO2, and CH4 were detected compared with levels in the atmospheric background and at the polygonal rims. The thickness of the salt crust ranges from approximately 0.3 to 1 m, with halite content primarily between 5 and 30 wt%, and is comparable in scale to the thickness (typically ❤ m) and abundance (10–25 wt%) of chloride deposits on Mars. These results suggest that similar salt crust formation should also be common in Martian crater basins subjected to long-term evaporation under hyperarid conditions. Furthermore, such salt crusts could trap deep volatiles, including potential biogenic gases, which may be detectable by gas spectrometers aboard Mars landers.

¹Claudia A. Trepmann,^1,2Fabian Dellefant,¹Lina Seybold,¹Wolfgang W. Schmahl,¹Elena Sturm,¹Daniel Weidendorfer,^1,3Sandro Jahn,¹Iuliia V. Sleptsova,¹Stuart A. Gilder
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70098]
¹Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Munich, Germany
²Department of Cultural and Ancient Studies, Ludwig-Maximilians-Universität München, Munich, Germany
³Mineralogical State Collection Munich (MSM), SNSB (Bavarian Natural History Collections), Munich, Germany
Published by arrangement with John Wiley & Sons

Calcite is prone to chemical and microstructural modifications, especially after having been strained at high stresses and strain rates, as during hypervelocity impact events. These modifications include precipitation from pore fluid as well as replacement of strained volumes by recrystallization. In calcite aggregates of a metagranite breccia of the Ries Bunte Breccia, shocked calcite is partly replaced by new, undeformed grains. This breccia indicates shock conditions of 10–20 GPa by the presence of planar deformation features in quartz of the metagranite. Shocked calcite shows grain orientation spread (GOS) angles of 3–10° and contains e-, f-, and r– twins, as well as a– and f-type lamellae. In contrast, the new coarse calcite grains, which are hundreds of μm in diameter, have low GOS angles (<1°), and do not contain twins. Calcite aggregates have a chemical zonation (varying Mnⁿ⁺ content), which is independent of new grains, suggestive of fast transformation. We propose that the new grains originate from sites of high crystal-plastic strain and grew by grain boundary migration driven by the reduction in strain energy, replacing previously strained grains at low stresses, that is, static recrystallization. Heating experiments on shocked calcite confirm the strain control on static recrystallization.