^1,2R. L. Cheng,^1,2J. R. Michalski,^3,4K. A. Campbell
Journal of Geophyiscal Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE007999]
¹Department of Earth Sciences, The University of Hong Kong, Hong Kong, China
²Laboratory for Space Research, The University of Hong Kong, Hong Kong, China
³School of Environment, The University of Auckland, Auckland, New Zealand
⁴Te Ao Mārama—Centre for Fundamental Inquiry, Faculty of Science, The University of Auckland, Auckland, New Zealand
Published by arrangement with John Wiley & Sons

Siliceous hot spring deposits, or sinters, deposit from hot spring discharge at Earth’s surface and are sites of exceptional preservation of biosignatures. Their macro- and micro-textures are regarded as important evidence of past microbial activities in hydrothermal environments. However, biology mimics do occur, and bona fide microbial textures could be destroyed by subsequent diagenesis or other post-depositional processes. Thus, it is paramount to narrow the search for prospective Martian silica-rich deposits that may contain biosignatures from both orbital and rover-based perspectives. This study investigates hydrothermal deposits in Chile, which are analogs of high-silica deposits discovered in the Gusev crater on Mars, through remote sensing and laboratory analysis. Results indicate that compositional remote sensing based on multispectral data with a high spatial resolution of <4 m/pixel reflects various concentrations of silica, which assisted in identifying the direction of discharged hydrothermal flows from the vent to the apron. Micro-infrared mapping of sinters from similar hydrothermal fields linked spectral features to specific textures revealed by scanning electron microscope and chemical compositions confirmed by electron microprobe analysis, indicating that sinters with no shift in their emissivity minimum in the thermal infrared range were more likely to preserve cellular structures. An instrument for collecting multispectral data with higher spatial resolution could aid in characterizing the geologic settings of potential hot springs on Mars. Locating emissivity minima in the infrared regions of silica that do not shift to a lower position would suggest the potential for well-preserved microbial structures in Martian sinters, if life ever did exist there.

¹Carolyn A. Crow,¹Cynthia Tong,²Timmons M. Erickson,³Desmond E. Moser,¹Aaron S. Bell,⁴Nigel M. Kelly,⁵Tabb C. Prissel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14162]
¹Department of Geological Sciences, University of Colorado Boulder, Boulder, Colorado, USA
²NASA JSC\Jacobs Technology, Houston, Texas, USA
³Western University, London, Ontario, Canada
⁴Bruker Corporation, Billerica, Massachusetts, USA
⁵NASA JSC, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

Investigations of trapped melt inclusions in minerals can yield insights into the compositions and conditions of parent magmas. These insights are particularly important for detrital grains like many of the lunar zircons found in samples returned by the Apollo missions. However, unlike their terrestrial counterparts, lunar zircons have potentially been exposed to billions of years of impact bombardment. Samples from terrestrial impact structures and impact shock experiments have revealed that deformation during an impact event produces melt and glass blebs that can mimic igneous melt inclusions in both morphology and composition. We have undertaken a geochemical and textural investigation of zircons from Apollo impact melt breccia 14311 to assess their formation mechanisms. The association of trapped melts with shock microtwins and monomineralic melt compositions suggests some inclusions formed as a result of the high pressures and temperatures of impact shock. All other inclusions in this study are associated with curviplanar features, planar features, crystal plastic deformation, or embayments (large regions in contact with adjacent melts or minerals) suggesting that they are not igneous melt inclusions. While these textures can be produced in tectonic environments, impacts are a likely formation mechanism since impacts are the main driver of tectonics on the Moon. The results of this study demonstrate that a combination of textural and compositional analyses can be employed distinguish between igneous melt inclusions and melt blebs in zircons from impact environments.