Mercury’s crust likely made of magnesium-rich basalt

With both x-ray and gamma-ray spectrometers, the MErcury Surface, Space ENvironment, GEochemistry and Ranging probe (MESSENGER), which entered orbit around Mercury in 2011, is well equipped for carrying out a detailed compositional analysis of Mercury’s crust, the understanding of which could help determine the nature of the planet’s formation, and of its volcanic past.

Using spectrometric measurements and laboratory analyzes of Mercury surface-analogue samples, Stockstill-Cahill et al. determine that the upper layers of Mercury’s crust most closely resemble magnesian basalt terrestrial rocks, though with lower iron concentrations. To make their determination, the authors used a software package known as MELTS to simulate the cooling and crystallization of potential Mercurian lavas with different chemical compositions, estimating the temperatures at which minerals would crystallize out of the molten lava and the abundances of different mineral species. Similarly, the authors simulated the cooling of magnesium-rich terrestrial rocks and of meteoritic samples.

Based on their chemical compositional analysis, the authors infer a number of properties for an early lava on Mercury. They suggest that the lava would have had a very low viscosity, streaming across the surface in widespread but thin layers. Further, they calculate that the temperatures required to produce the magnesium-rich lava would have been much higher than for terrestrial rocks not enriched in magnesium. The authors say that the low-viscosity lava would leave telltale marks on the planet’s surface that could be identified through further MESSENGER observations.

Source: Journal of Geophysical Research-Planets, doi: 10.1029/2012JE004140, 2012 http://onlinelibrary.wiley.com/doi/10.1029/2012JE004140/abstract

Title: Magnesium-rich crustal compositions on Mercury: Implications for magmatism from petrologic modeling

Authors: Karen R. Stockstill-Cahill and Timothy J. McCoy: Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, USA; Larry R. Nittler and Shoshana Z. Weider: Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, District of Columbia, USA; Steven A. Hauck, II: Department of Earth, Environmental, and Planetary Sciences, Case Western Reserve University, Cleveland, Ohio, USA.

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