2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 202-15
Presentation Time: 11:45 AM


CANNON, Kevin M. and MUSTARD, John F., Earth, Environmental, and Planetary Sciences, Brown University, Box 1846, Providence, RI 02912

Martian regolith is assumed to be made up of pulverized crystalline basalt. Under this paradigm, orbital spectroscopy data from martian low albedo (non dusty) regions are modeled as mixtures of olivine, pyroxene and plagioclase; however, these models must include unknown darkening agents and spectrally neutral components to properly fit the data. New micro-scale investigations hint at what these components could be: Curiosity rover CheMin measurements revealed up to 30% of martian soils and rocks are X-ray amorphous (modeled as mostly basaltic glass), and the first breccia meteorite from Mars, Northwest Africa (NWA) 7034, is the most chemically similar rock to bulk martian crust. Here we consider how these components (breccia and glass) can reconcile orbital spectral data with rover measurements and meteorites.

We measured the reflectance spectrum of NWA 7034 using both point spectroscopy and hyperspectral imaging, and we are measuring synthetic basaltic glasses with a variety of compositions and oxygen fugacities (fO2). NWA 7034’s spectrum is significantly darker and more spectrally neutral than all other martian meteorites, with attenuated absorption bands near 1 and 2 μm and a negative spectral slope. We hypothesize this is caused by NWA 7034’s extremely fine-grained matrix that overwhelms the spectral signature of embedded pyroxene and plagioclase clasts. Similarly, basaltic glass spectra are dark with broad, weak crystal-field absorptions near 1 and 2 μm distinct from those of pyroxene and olivine. The position and strength of these bands depend on the glass structure and fO2.

We suggest a new approach to explain global spectral observations of martian low-albedo regions. In this model, the regolith in these regions consists mostly of sand-sized particles of: basalt (crystalline, spectrally active), brecciated rocks (crystalline, spectrally neutral) and basaltic glass (amorphous, spectrally neutral). This is consistent with previous studies showing that spectral matches to the SNC meteorites (unbrecciated) are restricted to minor rocky patches in the low albedo regions. We will test this new model with our laboratory spectral measurements and global spectroscopy data to constrain relative proportions of these three components and achieve consistency between micro- and mega-scale measurements.