THE GLOBAL DISTRIBUTION OF GLASS IN MARTIAN DUNES AND IMPLICATIONS FOR THE ORIGIN OF SAND ON MARS

Erosion by sand has shaped the martian surface, and dune fields are abundant on Mars today. However, the origin of martian sand is still not well understood. Here we constrain the origin and alteration history of sands on Mars by investigating the global composition of martian dunes. In particular, we seek to better understand the distribution of glass and secondary amorphous materials, which we hypothesize may be important components of global dunes based on local spectral studies and in situ investigation by MSL.

We use a combination of orbital visible/near-infrared (VNIR) and thermal infrared (TIR) spectra, and apply techniques optimized to detect amorphous materials: (1) analysis of the position and shape of VNIR iron bands to detect glass, and (2) a new TIR spectral library with additional glass and secondary amorphous endmembers. CRISM spectra were extracted from 41 dune fields between 70N-70S and compared to OMEGA spectra from the north polar sand sea. TES spectra from 90 dune fields between 75N-75S produced high-quality fits when deconvolved using our spectral library.

We find that the north polar sand sea and 20% of small dune fields exhibit VNIR spectra consistent with glass, and up to 34% may contain a significant glass component. In TES spectral models, 15% of dune fields contain significant glass (10-50% of primary minerals) and another 15% of dune fields have alteration components that are dominated by amorphous silicates. Notably, all dune fields exhibit high abundances of alteration products (avg. 54%).

Amorphous materials are found at all latitudes in both data sets, but high abundances of glass, secondary amorphous materials, and crystalline alteration products are more common at high latitudes. A lack of TES glass detections in locations with clear VNIR glass detections suggests that alteration may be in the form of a coating obscuring the substrate at TIR wavelengths. Glass and amorphous alteration products are anti-correlated in individual dune fields, consistent with previous suggestions that removal of the coating during saltation may reveal the underlying glass. Glass abundances at high latitudes could be enhanced by ice-magma interactions and by long-term buildup of impact spherules. Enhanced secondary amorphous materials at high latitudes may be related to periglacial weathering.

Our results show that glass and secondary amorphous materials are an important component of global dunes, suggesting a major role for impact, volcanic, and weathering processes in the sedimentary cycle of Mars.