Serpentine-magnesite Association of Salem Ultramafic Complex, Southern India: A Potential Analogue for Mars

Abstract

The primary mineral olivine and its alteration products, serpentine and magnesite, have been reported from several locales on Mars. The mineralogical similarity of the altered ultramafic rocks on Earth makes them a potential analogue that can provide significant insight into the serpentinization and carbonation processes on Mars. This serpentine-magnesite assemblage is significant in astrobiology because serpentinization is known for the formation of simple organic molecules like methane from inorganic precursors. An association of olivine-serpentine-magnesite is widely distributed in the Salem Ultramafic Complex (SUC) in Southern India. We used hyperspectral, Laser Raman, and Fourier-transform infrared (FTIR) techniques to characterize this mineral association in the SUC. The visible and near-infrared (VNIR) spectra of all the serpentine samples show a narrow and strong absorption feature at 1.4 ​μm and an in-depth feature at 2.35 ​μm. Magnesite samples have broad and strong features at 1.4 ​μm, 2.3 ​μm, and 2.5 ​μm. The obtained spectra were compared with their Martian counterparts using the Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) type spectral library. Raman spectroscopy is used to differentiate serpentine polymorphs. The major polymorph in the area is antigorite, which shows intense Raman peaks at 682 ​cm −1 , 371 ​cm −1 , and 228 ​cm −1 , and weak peaks at 635 ​cm −1 and 1040 ​cm −1 . The Raman peaks at 1096 ​cm −1 and 326 ​cm −1 are typical of magnesite. FTIR spectra from the serpentine samples are characterized by the absorption feature at 3680 ​cm −1 indicative of antigorite, formed due to hydroxyl stretching. Diagnostic absorption features of magnesite are observed at 748 ​cm −1 , 877 ​cm −1 , 1427 ​cm −1 , 1826 ​cm −1 , and 2358 ​cm −1 . The results from this study can be applied to future missions to validate orbital spectroscopic data, instrument calibration purposes, and data interpretation. • The Serpentine-magnesite assemblage in Salem Ultramafic Complex (SUC) in Southern India is considered as a potential Martian analogue site. • Spectral and chemical characterization of the serpentine-magnesite assemblage. • The study compares serpentine-magnesite assemblage of SUC to those of Mars from an astrobiological and geochemical point of view. • Future Mars missions can use the results to validate orbital spectroscopic data, for instrument calibration purposes, and for data interpretation.