¹Adnan Ahmad,¹Raj Patel,¹Bhaswati Deka,²Rohit Nagori,²A.S.Arya,¹Archana M.Nair
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114953]
¹Department of Civil Engineering, Indian Institute of Technology Guwahati, Assam, India
²Space Application Centre, Indian Space Research Organization, Ahmedabad, India
Copyright Elsevier

Identification of phyllosilicates on Mars suggests the existence of an aqueous environment, indicating an active period in its evolutionary history. This study analysed the surface mineralogy of caldera and flank regions of Tharsis Montes using remote spectral analysis. Though a thick layer of dust obscures the surface of Tharsis volcanic province, relatively lesser dust regions provide a unique window for exploration. The reflectance data obtained from CRISM onboard Mars Reconnaissance Orbiter in the visible-infrared region is used for the mineralogical study. Spectral parameter indices were used to identify the distribution of minerals over the caldera and flank regions of Tharsis Montes. The spectral characterisation indicates the well-distributed presence of mafic minerals such as olivine with low-calcium pyroxene and plagioclase with the sparse presence of high-calcium pyroxene in the region. The dusty region, typically with a high TES DCI index and low thermal inertia values in the Tharsis Montes, shows a high concentration of olivine. Few regions identified as comparatively dust-free at the caldera and flank show the presence of secondary mafic minerals like Fesingle bondMg bearing phyllosilicates. Our spectral analysis using nonlinear mixing models with the MICA spectral library indicates the occurrence of absorption features characteristic of hydrated minerals. The occurrence of the secondary mafic minerals, especially the phyllosilicates on Tharsis Montes suggest active weathering or hydrothermal alteration from episodic volcanic activity over time. Many factors on the Martian surface obstruct clean and noise-free data acquisition, pointing to the necessity of validating interpretations using multiple data sets.

¹Sheng Shang,^1,2Hejiu Hui,²Yueheng Yang,¹Tianyu Chen
Earth and Planetary Science Letters 581, 117413 Link to Article [https://doi.org/10.1016/j.epsl.2022.117413]
¹State Key Laboratory for Mineral Deposits Research & Lunar and Planetary Science Institute, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
²CAS Center for Excellence in Comparative Planetology, Hefei 230026, China
³State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Copyright Elsevier

The observations of Martian orbiters and rovers have suggested that there were fluids on the surface of early Mars. However, the geochemical properties of those fluids are unclear. The Martian regolith breccia meteorites (MRB), the source materials of which are thought to have formed at 4.4 Ga, may have recorded interactions with fluids on Mars. Here, we have analyzed the in situ Sm-Nd isotopic compositions and trace element contents of apatite in MRB and have obtained a Sm-Nd isochron age of 1490±480 Ma. This young age indicates that the MRB apatites were altered by fluids and have exchanged trace elements with fluids. The very negative initial Nd, combined with the previously reported positive δD and Cl in the MRB apatites, indicate that Martian fluids originated from a geochemically enriched reservoir in the crust. The large ranges of rare earth element abundance (ΣREE) and of the chondrite normalized ratio of La and Yb [(La/Yb)N] indicate the chemical complexity of the fluids that interacted with the apatites in the MRB. The apatite REE compositions were used to further determine the pH values of Martian fluids equilibrated with the MRB apatites, which varied from ∼3 to ∼8. The apatite X-site Cl contents indicate that the Cl contents in Martian fluids in equilibrium with the MRB apatites at 400 °C and 1 bar could be up to 1857 ppm, within the range of terrestrial hydrothermal fluids. Combined with previously reported geochemical data from Martian meteorites, our study suggests that fluids may have been present throughout the early geological history of Mars.