Silica deposits in the Nili Patera caldera on the Syrtis Major volcanic complex on Mars

Journal name:
Nature Geoscience
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The martian surface features abundant volcanoes and evidence for past liquid water. Extant or relict martian volcanic hydrothermal systems have therefore been sought in the pursuit of evidence for habitable environments1. The Mars Exploration Rover, Spirit, detected deposits highly enriched in silica with accessory minerals, suggesting formation by hydrothermal leaching of basaltic rocks by low-pH solutions2. However, extensive erosion has obscured the context of the formation environment of these deposits. Silica deposits have also been identified remotely, but also with limited contextual clues to their formation; aqueous alteration products of basalt and volcanic ash are the most likely sources3, 4. Here we report the detection from orbit of hydrated silica deposits on the flanks of a volcanic cone in the martian Syrtis Major caldera complex. Near-infrared observations show dozens of localized hydrated silica deposits. As a result of the morphology of these deposits and their location in and around the cone summit, we suggest that the deposits were produced by a volcanically driven hydrothermal system. The cone and associated lava flows post-date Early Hesperian volcano formation. We conclude that, if a relict hydrothermal system was associated with the silica deposits, it may preserve one of the most recent habitable microenvironments on Mars.

At a glance


  1. Image of the Nili Patera caldera in Syrtis Major.
    Figure 1: Image of the Nili Patera caldera in Syrtis Major.

    a, CTX greyscale imagery overlain with a decorrelation stretch of Thermal Emission Imaging System (THEMIS) bands 9, 7 and 5. The pink regions correspond with Si-enriched areas as indicated by deconvolution of Thermal Emission Spectrometer spectra9. b, Cone structure; arrows indicate the largest of the deposits discussed in this Letter. However, all of the bright areas to the left of the arrows exhibit similar spectral features if they are large enough to fill a CRISM pixel. (CTX: P04_002427_1888_XI_08N292W; THEMIS: I09472026 (ref. 30)).

  2. CRISM and HiRISE observations of silica deposits.
    Figure 2: CRISM and HiRISE observations of silica deposits.

    a, CRISM red–green–blue composite (red: 2.4μm, green: 1.5μm, blue: 1.1μm) of the Nili Patera cone with deposits (image FRT00010628). The CRISM images are ~10km across at the centre. b, Custom 2.2μm band depth map with magenta indicating detections. The large black ellipse indicates a large field with many discrete deposits; the small black ellipse indicates summit deposits. The blue, green and red arrows correspond to the deposit spectra shown in Fig. 3. c, HiRISE image of a flank deposit showing a fan shape. d, HiRISE image of a floor deposit to the south of the cone showing a typical semicircular shape (HiRISE: ESP_013582_1895).

  3. Mineral deposit spectra indicative of Si-OH.
    Figure 3: Mineral deposit spectra indicative of Si–OH.

    a, Calibrated spectra of the unit indicated by the red arrow in Fig. 2b and the corresponding denominator spectra. The most distinctive feature is the absorption band at 2.2μm. b, Ratioed spectra from the regions indicated by the coloured arrows in Fig. 2. Detection is based on the characteristic absorption at 2.2μm. c, Average ratioed spectra from regions of interest that include all bright deposits (magenta in Fig. 2b). The arrows indicate possible weak water absorptions at 1.4 and 1.9μm. A laboratory spectrum of silica-coated basalt is shown for comparison15. Note the similar 2.2μm Si–OH absorption. The strong increase in reflectance of the library sample at low wavelengths is due to the presence of Fe3+ not seen in the Mars data.


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  1. Department of Geological Sciences, Box 1846, Brown University, Providence, Rhode Island 02912, USA

    • J. R. Skok,
    • J. F. Mustard &
    • B. L. Ehlmann
  2. Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, Indiana 46556, USA

    • R. E. Milliken
  3. John Hopkins University, Applied Physics Laboratory, Laurel, Maryland 20723, USA

    • S. L. Murchie


J.R.S. initiated the study, conducted the analysis and wrote manuscript. J.F.M. provided guidance, improved analysis and defined the focus of the work. B.L.E. contributed significantly to the analysis and manuscript contributions. R.E.M. provided research background and technique guidance. S.L.M. was responsible for data acquisition and manuscript refinement.

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